Logical Volume Manager Administration

Red Hat Enterprise Linux 6
Logical Volume Manager Administration
LVM Administrator Guide
Last Updated: 2018-02-08
Red Hat Enterprise Linux 6 Logical Volume Manager Administration
LVM Administrator Guide
Steven Levine
Red Hat Customer Content Services
slevine@redhat.com
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Abstract
This book describes the LVM logical volume manager, including information on running LVM in a
clustered environment.
Table of Contents
Table of Contents
.CHAPTER
. . . . . . . . .1.. .INTRODUCTION
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7. . . . . . . . . .
1.1. AUDIENCE
7
1.2. SOFTWARE VERSIONS
7
1.3. RELATED DOCUMENTATION
7
1.4. WE NEED FEEDBACK!
8
.CHAPTER
. . . . . . . . .2.. .THE
. . . .LVM
. . . . LOGICAL
. . . . . . . . .VOLUME
. . . . . . . .MANAGER
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9. . . . . . . . . .
2.1. NEW AND CHANGED FEATURES
9
2.1.1. New and Changed Features for Red Hat Enterprise Linux 6.0
9
2.1.2. New and Changed Features for Red Hat Enterprise Linux 6.1
10
2.1.3. New and Changed Features for Red Hat Enterprise Linux 6.2
10
2.1.4. New and Changed Features for Red Hat Enterprise Linux 6.3
11
2.1.5. New and Changed Features for Red Hat Enterprise Linux 6.4
11
2.1.6. New and Changed Features for Red Hat Enterprise Linux 6.5
11
2.1.7. New and Changed Features for Red Hat Enterprise Linux 6.6
12
2.1.8. New and Changed Features for Red Hat Enterprise Linux 6.7
2.1.9. New and Changed Features for Red Hat Enterprise Linux 6.8
13
13
2.2. LOGICAL VOLUMES
2.3. LVM ARCHITECTURE OVERVIEW
13
14
2.4. THE CLUSTERED LOGICAL VOLUME MANAGER (CLVM)
2.5. DOCUMENT OVERVIEW
15
17
. . . . . . . . . .3.. .LVM
CHAPTER
. . . .COMPONENTS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
...........
3.1. PHYSICAL VOLUMES
3.1.1. LVM Physical Volume Layout
19
19
3.1.2. Multiple Partitions on a Disk
3.2. VOLUME GROUPS
20
20
3.3. LVM LOGICAL VOLUMES
3.3.1. Linear Volumes
3.3.2. Striped Logical Volumes
21
21
23
3.3.3. Mirrored Logical Volumes
3.3.4. RAID Logical Volumes
3.3.5. Thinly-Provisioned Logical Volumes (Thin Volumes)
3.3.6. Snapshot Volumes
3.3.7. Thinly-Provisioned Snapshot Volumes
24
24
25
25
26
3.3.8. Cache Volumes
27
.CHAPTER
. . . . . . . . .4.. .LVM
. . . .ADMINISTRATION
. . . . . . . . . . . . . . . . OVERVIEW
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
...........
4.1. CREATING LVM VOLUMES IN A CLUSTER
28
4.2. LOGICAL VOLUME CREATION OVERVIEW
28
4.3. GROWING A FILE SYSTEM ON A LOGICAL VOLUME
29
4.4. LOGICAL VOLUME BACKUP
4.5. LOGGING
4.6. THE METADATA DAEMON (LVMETAD)
4.7. DISPLAYING LVM INFORMATION WITH THE LVM COMMAND
29
30
30
31
.CHAPTER
. . . . . . . . .5.. .LVM
. . . .ADMINISTRATION
. . . . . . . . . . . . . . . . WITH
. . . . . CLI
. . . .COMMANDS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
...........
5.1. USING CLI COMMANDS
32
5.2. PHYSICAL VOLUME ADMINISTRATION
5.2.1. Creating Physical Volumes
5.2.1.1. Setting the Partition Type
5.2.1.2. Initializing Physical Volumes
33
33
33
34
1
Logical Volume Manager Administration
5.2.1.3. Scanning for Block Devices
5.2.2. Displaying Physical Volumes
5.2.3. Preventing Allocation on a Physical Volume
5.2.4. Resizing a Physical Volume
5.2.5. Removing Physical Volumes
5.3. VOLUME GROUP ADMINISTRATION
5.3.1. Creating Volume Groups
36
36
36
36
5.3.2. LVM Allocation
5.3.3. Creating Volume Groups in a Cluster
5.3.4. Adding Physical Volumes to a Volume Group
5.3.5. Displaying Volume Groups
37
38
39
39
5.3.6. Scanning Disks for Volume Groups to Build the Cache File
5.3.7. Removing Physical Volumes from a Volume Group
5.3.8. Changing the Parameters of a Volume Group
5.3.9. Activating and Deactivating Volume Groups
5.3.10. Removing Volume Groups
40
40
41
41
42
5.3.11. Splitting a Volume Group
5.3.12. Combining Volume Groups
5.3.13. Backing Up Volume Group Metadata
42
42
42
5.3.14. Renaming a Volume Group
5.3.15. Moving a Volume Group to Another System
43
43
5.3.16. Recreating a Volume Group Directory
5.4. LOGICAL VOLUME ADMINISTRATION
44
44
5.4.1. Creating Linear Logical Volumes
44
5.4.2. Creating Striped Volumes
5.4.3. Creating Mirrored Volumes
45
46
5.4.3.1. Mirrored Logical Volume Failure Policy
49
5.4.3.2. Splitting Off a Redundant Image of a Mirrored Logical Volume
5.4.3.3. Repairing a Mirrored Logical Device
49
50
5.4.3.4. Changing Mirrored Volume Configuration
5.4.4. Creating Thinly-Provisioned Logical Volumes
50
51
5.4.5. Creating Snapshot Volumes
53
5.4.6. Creating Thinly-Provisioned Snapshot Volumes
5.4.7. Creating LVM Cache Logical Volumes
55
57
5.4.8. Merging Snapshot Volumes
5.4.9. Persistent Device Numbers
59
59
5.4.10. Changing the Parameters of a Logical Volume Group
60
5.4.11. Renaming Logical Volumes
5.4.12. Removing Logical Volumes
60
60
5.4.13. Displaying Logical Volumes
60
5.4.14. Growing Logical Volumes
5.4.14.1. Extending a Striped Volume
61
62
5.4.14.2. Extending a Mirrored Volume
5.4.14.3. Extending a Logical Volume with the cling Allocation Policy
2
34
35
35
63
64
5.4.15. Shrinking Logical Volumes
66
5.4.16. RAID Logical Volumes
5.4.16.1. Creating a RAID Logical Volume
67
68
5.4.16.2. Converting a Linear Device to a RAID Device
5.4.16.3. Converting an LVM RAID1 Logical Volume to an LVM Linear Logical Volume
70
71
5.4.16.4. Converting a Mirrored LVM Device to a RAID1 Device
72
5.4.16.5. Changing the Number of Images in an Existing RAID1 Device
5.4.16.6. Splitting off a RAID Image as a Separate Logical Volume
72
75
5.4.16.7. Splitting and Merging a RAID Image
76
Table of Contents
5.4.16.8. Setting a RAID fault policy
5.4.16.8.1. The allocate RAID Fault Policy
78
78
5.4.16.8.2. The warn RAID Fault Policy
5.4.16.9. Replacing a RAID device
80
81
5.4.16.10. Scrubbing a RAID Logical Volume
82
5.4.16.11. Controlling I/O Operations on a RAID1 Logical Volume
5.4.17. Controlling Logical Volume Activation
84
84
5.5. CONTROLLING LVM DEVICE SCANS WITH FILTERS
85
5.6. ONLINE DATA RELOCATION
5.7. ACTIVATING LOGICAL VOLUMES ON INDIVIDUAL NODES IN A CLUSTER
86
87
5.8. CUSTOMIZED REPORTING FOR LVM
5.8.1. Format Control
87
87
5.8.2. Object Selection
89
The pvs Command
The vgs Command
90
92
The lvs Command
5.8.3. Sorting LVM Reports
93
97
5.8.4. Specifying Units
98
. . . . . . . . . .6.. .LVM
CHAPTER
. . . .CONFIGURATION
. . . . . . . . . . . . . . . .EXAMPLES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
............
6.1. CREATING AN LVM LOGICAL VOLUME ON THREE DISKS
6.1.1. Creating the Physical Volumes
100
100
6.1.2. Creating the Volume Group
100
6.1.3. Creating the Logical Volume
6.1.4. Creating the File System
100
100
6.2. CREATING A STRIPED LOGICAL VOLUME
6.2.1. Creating the Physical Volumes
101
101
6.2.2. Creating the Volume Group
101
6.2.3. Creating the Logical Volume
6.2.4. Creating the File System
102
102
6.3. SPLITTING A VOLUME GROUP
6.3.1. Determining Free Space
102
103
6.3.2. Moving the Data
103
6.3.3. Splitting the Volume Group
6.3.4. Creating the New Logical Volume
103
104
6.3.5. Making a File System and Mounting the New Logical Volume
6.3.6. Activating and Mounting the Original Logical Volume
104
104
6.4. REMOVING A DISK FROM A LOGICAL VOLUME
105
6.4.1. Moving Extents to Existing Physical Volumes
105
6.4.2. Moving Extents to a New Disk
6.4.2.1. Creating the New Physical Volume
105
106
6.4.2.2. Adding the New Physical Volume to the Volume Group
106
6.4.2.3. Moving the Data
106
6.4.2.4. Removing the Old Physical Volume from the Volume Group
106
6.5. CREATING A MIRRORED LVM LOGICAL VOLUME IN A CLUSTER
107
. . . . . . . . . .7.. .LVM
CHAPTER
. . . .TROUBLESHOOTING
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
............
7.1. TROUBLESHOOTING DIAGNOSTICS
7.2. DISPLAYING INFORMATION ON FAILED DEVICES
110
110
7.3. RECOVERING FROM LVM MIRROR FAILURE
111
7.4. RECOVERING PHYSICAL VOLUME METADATA
114
7.5. REPLACING A MISSING PHYSICAL VOLUME
116
7.6. REMOVING LOST PHYSICAL VOLUMES FROM A VOLUME GROUP
116
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Logical Volume Manager Administration
7.7. INSUFFICIENT FREE EXTENTS FOR A LOGICAL VOLUME
7.8. DUPLICATE PV WARNINGS FOR MULTIPATHED DEVICES
116
117
7.8.1. Root Cause of Duplicate PV Warning
117
7.8.2. Duplicate Warnings for Single Paths
118
7.8.3. Duplicate Warnings for Multipath Maps
119
. . . . . . . . . .8.. .LVM
CHAPTER
. . . .ADMINISTRATION
. . . . . . . . . . . . . . . . WITH
. . . . . THE
. . . . LVM
. . . . .GUI
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
............
. . . . . . . . . . A.
APPENDIX
. . .THE
. . . .DEVICE
. . . . . . .MAPPER
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
............
A.1. DEVICE TABLE MAPPINGS
A.1.1. The linear Mapping Target
121
122
A.1.2. The striped Mapping Target
122
A.1.3. The mirror Mapping Target
124
A.1.4. The snapshot and snapshot-origin Mapping Targets
126
A.1.5. The error Mapping Target
128
A.1.6. The zero Mapping Target
A.1.7. The multipath Mapping Target
128
128
A.1.8. The crypt Mapping Target
131
A.1.9. The device-mapper RAID Mapping Target
132
A.1.10. The thin and thin-pool Mapping Targets
135
A.2. THE DMSETUP COMMAND
A.2.1. The dmsetup info Command
137
137
A.2.2. The dmsetup ls Command
139
A.2.3. The dmsetup status Command
140
A.2.4. The dmsetup deps Command
140
A.3. DEVICE MAPPER SUPPORT FOR THE UDEV DEVICE MANAGER
A.3.1. udev Integration with the Device Mapper
A.3.2. Commands and Interfaces that Support udev
141
141
143
. . . . . . . . . . B.
APPENDIX
. . .THE
. . . .LVM
. . . .CONFIGURATION
. . . . . . . . . . . . . . . .FILES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145
............
B.1. THE LVM CONFIGURATION FILES
145
B.2. THE LVMCONFIG COMMAND
145
B.3. LVM PROFILES
B.4. SAMPLE LVM.CONF FILE
146
147
. . . . . . . . . . C.
APPENDIX
. . .LVM
. . . .SELECTION
. . . . . . . . . . .CRITERIA
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168
............
C.1. SELECTION CRITERIA FIELD TYPES
168
C.2. SELECTION CRITERIA OPERATORS
169
C.3. SELECTION CRITERIA FIELDS
171
C.3.1. Specifying Time Values
C.3.1.1. Standard time selection format
183
183
C.3.1.2. Freeform time selection format
184
C.4. SELECTION CRITERIA DISPLAY EXAMPLES
185
C.5. SELECTION CRITERIA PROCESSING EXAMPLES
187
. . . . . . . . . . D.
APPENDIX
. . .LVM
. . . .OBJECT
. . . . . . . .TAGS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .190
............
D.1. ADDING AND REMOVING OBJECT TAGS
190
D.2. HOST TAGS
D.3. CONTROLLING ACTIVATION WITH TAGS
190
191
. . . . . . . . . . E.
APPENDIX
. . LVM
. . . . .VOLUME
. . . . . . . .GROUP
. . . . . . . METADATA
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192
............
4
E.1. THE PHYSICAL VOLUME LABEL
192
E.2. METADATA CONTENTS
192
E.3. SAMPLE METADATA
193
Table of Contents
. . . . . . . . . . F.
APPENDIX
. . REVISION
. . . . . . . . . HISTORY
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .196
............
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197
INDEX
............
5
Logical Volume Manager Administration
6
CHAPTER 1. INTRODUCTION
CHAPTER 1. INTRODUCTION
This book describes the Logical Volume Manager (LVM), including information on running LVM in a
clustered environment.
1.1. AUDIENCE
This book is intended to be used by system administrators managing systems running the Linux
operating system. It requires familiarity with Red Hat Enterprise Linux 6.
1.2. SOFTWARE VERSIONS
Table 1.1. Software Versions
Software
Description
Red Hat Enterprise
Linux 6
refers to Red Hat Enterprise Linux 6 and higher
GFS2
refers to GFS2 for Red Hat Enterprise Linux 6 and higher
1.3. RELATED DOCUMENTATION
For more information about using Red Hat Enterprise Linux, see the following resources:
Installation Guide — Documents relevant information regarding the installation of Red Hat
Enterprise Linux 6.
Deployment Guide — Documents relevant information regarding the deployment, configuration
and administration of Red Hat Enterprise Linux 6.
Storage Administration Guide — Provides instructions on how to effectively manage storage
devices and file systems on Red Hat Enterprise Linux 6.
For more information about the High Availability Add-On and the Resilient Storage Add-On for Red Hat
Enterprise Linux 6, see the following resources:
High Availability Add-On Overview — Provides a high-level overview of the Red Hat High
Availability Add-On.
Cluster Administration — Provides information about installing, configuring and managing the
Red Hat High Availability Add-On,
Global File System 2: Configuration and Administration — Provides information about installing,
configuring, and maintaining Red Hat GFS2 (Red Hat Global File System 2), which is included in
the Resilient Storage Add-On.
DM Multipath — Provides information about using the Device-Mapper Multipath feature of Red
Hat Enterprise Linux 6.
Load Balancer Administration — Provides information on configuring high-performance systems
and services with the Load Balancer Add-On, a set of integrated software components that
provide Linux Virtual Servers (LVS) for balancing IP load across a set of real servers.
7
Logical Volume Manager Administration
Release Notes — Provides information about the current release of Red Hat products.
Red Hat documents are available in HTML, PDF, and RPM versions on the Red Hat Enterprise Linux
Documentation CD and online at https://access.redhat.com/site/documentation/.
1.4. WE NEED FEEDBACK!
If you find a typographical error in this manual, or if you have thought of a way to make this manual
better, we would love to hear from you! Please submit a report in Bugzilla: http://bugzilla.redhat.com/
against the product Red Hat Enterprise Linux 6 and the component doc-Logical_Volume_Manager.
When submitting a bug report, be sure to mention the manual's identifier:
Logical_Volume_Manager_Administration(EN)-6 (2017-3-8-15:20)
If you have a suggestion for improving the documentation, try to be as specific as possible when
describing it. If you have found an error, include the section number and some of the surrounding text so
we can find it easily.
8
CHAPTER 2. THE LVM LOGICAL VOLUME MANAGER
CHAPTER 2. THE LVM LOGICAL VOLUME MANAGER
This chapter provides a summary of the features of the LVM logical volume manager that are new for the
initial and subsequent releases of Red Hat Enterprise Linux 6. Following that, this chapter provides a
high-level overview of the components of the Logical Volume Manager (LVM).
2.1. NEW AND CHANGED FEATURES
This section lists new and changed features of the LVM logical volume manager that are included with
the initial and subsequent releases of Red Hat Enterprise Linux 6.
2.1.1. New and Changed Features for Red Hat Enterprise Linux 6.0
Red Hat Enterprise Linux 6.0 includes the following documentation and feature updates and changes.
You can define how a mirrored logical volume behaves in the event of a device failure with the
mirror_image_fault_policy and mirror_log_fault_policy parameters in the
activation section of the lvm.conf file. When this parameter is set to remove, the system
attempts to remove the faulty device and run without it. When this parameter is set to
allocate, the system attempts to remove the faulty device and tries to allocate space on a new
device to be a replacement for the failed device; this policy acts like the remove policy if no
suitable device and space can be allocated for the replacement. For information on the LVM
mirror failure policies, see Section 5.4.3.1, “Mirrored Logical Volume Failure Policy”.
For the Red Hat Enterprise Linux 6 release, the Linux I/O stack has been enhanced to process
vendor-provided I/O limit information. This allows storage management tools, including LVM, to
optimize data placement and access. This support can be disabled by changing the default
values of data_alignment_detection and data_alignment_offset_detection in the
lvm.conf file, although disabling this support is not recommended.
For information on data alignment in LVM as well as information on changing the default values
of data_alignment_detection and data_alignment_offset_detection, see the inline
documentation for the /etc/lvm/lvm.conf file, which is also documented in Appendix B, The
LVM Configuration Files. For general information on support for the I/O Stack and I/O limits in
Red Hat Enterprise Linux 6, see the Storage Administration Guide.
In Red Hat Enterprise Linux 6, the Device Mapper provides direct support for udev integration.
This synchronizes the Device Mapper with all udev processing related to Device Mapper
devices, including LVM devices. For information on Device Mapper support for the udev device
manager, see Section A.3, “Device Mapper Support for the udev Device Manager”.
For the Red Hat Enterprise Linux 6 release, you can use the lvconvert --repair command
to repair a mirror after disk failure. This brings the mirror back into a consistent state. For
information on the lvconvert --repair command, see Section 5.4.3.3, “Repairing a
Mirrored Logical Device”.
As of the Red Hat Enterprise Linux 6 release, you can use the --merge option of the
lvconvert command to merge a snapshot into its origin volume. For information on merging
snapshots, see Section 5.4.8, “Merging Snapshot Volumes”.
As of the Red Hat Enterprise Linux 6 release, you can use the --splitmirrors argument of
the lvconvert command to split off a redundant image of a mirrored logical volume to form a
new logical volume. For information on using this option, see Section 5.4.3.2, “Splitting Off a
Redundant Image of a Mirrored Logical Volume”.
9
Logical Volume Manager Administration
You can now create a mirror log for a mirrored logical device that is itself mirrored by using the -mirrorlog mirrored argument of the lvcreate command when creating a mirrored logical
device. For information on using this option, see Section 5.4.3, “Creating Mirrored Volumes”.
2.1.2. New and Changed Features for Red Hat Enterprise Linux 6.1
Red Hat Enterprise Linux 6.1 includes the following documentation and feature updates and changes.
The Red Hat Enterprise Linux 6.1 release supports the creation of snapshot logical volumes of
mirrored logical volumes. You create a snapshot of a mirrored volume just as you would create
a snapshot of a linear or striped logical volume. For information on creating snapshot volumes,
see Section 5.4.5, “Creating Snapshot Volumes”.
When extending an LVM volume, you can now use the --alloc cling option of the
lvextend command to specify the cling allocation policy. This policy will choose space on the
same physical volumes as the last segment of the existing logical volume. If there is insufficient
space on the physical volumes and a list of tags is defined in the lvm.conf file, LVM will check
whether any of the tags are attached to the physical volumes and seek to match those physical
volume tags between existing extents and new extents.
For information on extending LVM mirrored volumes with the --alloc cling option of the
lvextend command, see Section 5.4.14.3, “Extending a Logical Volume with the cling
Allocation Policy”.
You can now specify multiple --addtag and --deltag arguments within a single pvchange,
vgchange, or lvchange command. For information on adding and removing object tags, see
Section D.1, “Adding and Removing Object Tags”.
The list of allowed characters in LVM object tags has been extended, and tags can contain the
"/", "=", "!", ":", "#", and "&" characters. For information on LVM object tags, see Appendix D,
LVM Object Tags.
You can now combine RAID0 (striping) and RAID1 (mirroring) in a single logical volume.
Creating a logical volume while simultaneously specifying the number of mirrors (--mirrors
X) and the number of stripes (--stripes Y) results in a mirror device whose constituent
devices are striped. For information on creating mirrored logical volumes, see Section 5.4.3,
“Creating Mirrored Volumes”.
As of the Red Hat Enterprise Linux 6.1 release, if you need to create a consistent backup of data
on a clustered logical volume you can activate the volume exclusively and then create the
snapshot. For information on activating logical volumes exclusively on one node, see
Section 5.7, “Activating Logical Volumes on Individual Nodes in a Cluster”.
2.1.3. New and Changed Features for Red Hat Enterprise Linux 6.2
Red Hat Enterprise Linux 6.2 includes the following documentation and feature updates and changes.
The Red Hat Enterprise Linux 6.2 release supports the issue_discards parameter in the
lvm.conf configuration file. When this parameter is set, LVM will issue discards to a logical
volume's underlying physical volumes when the logical volume is no longer using the space on
the physical volumes. For information on this parameter, see the inline documentation for the
/etc/lvm/lvm.conf file, which is also documented in Appendix B, The LVM Configuration
Files.
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2.1.4. New and Changed Features for Red Hat Enterprise Linux 6.3
Red Hat Enterprise Linux 6.3 includes the following documentation and feature updates and changes.
As of the Red Hat Enterprise Linux 6.3 release, LVM supports RAID4/5/6 and a new
implementation of mirroring. For information on RAID logical volumes, see Section 5.4.16, “RAID
Logical Volumes”.
When you are creating a new mirror that does not need to be revived, you can specify the -nosync argument to indicate that an initial synchronization from the first device is not required.
For information on creating mirrored volumes, see Section 5.4.3, “Creating Mirrored Volumes”.
This manual now documents the snapshot autoextend feature. For information on creating
snapshot volumes, see Section 5.4.5, “Creating Snapshot Volumes”.
2.1.5. New and Changed Features for Red Hat Enterprise Linux 6.4
Red Hat Enterprise Linux 6.4 includes the following documentation and feature updates and changes.
Logical volumes can now be thinly provisioned. This allows you to create logical volumes that
are larger than the available extents. Using thin provisioning, you can manage a storage pool of
free space, known as a thin pool, to be allocated to an arbitrary number of devices when needed
by applications. You can then create devices that can be bound to the thin pool for later
allocation when an application actually writes to the logical volume. The thin pool can be
expanded dynamically when needed for cost-effective allocation of storage space.
For general information on thinly-provisioned logical volumes, see Section 3.3.5, “ThinlyProvisioned Logical Volumes (Thin Volumes)”. For information on creating thin volumes, see
Section 5.4.4, “Creating Thinly-Provisioned Logical Volumes”.
The Red Hat Enterprise Linux release 6.4 version of LVM provides support for thinly-provisioned
snapshot volumes. Thin snapshot volumes allow many virtual devices to be stored on the same
data volume. This simplifies administration and allows for the sharing of data between snapshot
volumes.
For general information on thinly-provisioned snapshot volumes, see Section 3.3.7, “ThinlyProvisioned Snapshot Volumes”. For information on creating thin snapshot volumes, see
Section 5.4.6, “Creating Thinly-Provisioned Snapshot Volumes”.
This document includes a new section detailing LVM allocation policy, Section 5.3.2, “LVM
Allocation”.
LVM now provides support for raid10 logical volumes. For information on RAID logical
volumes, see Section 5.4.16, “RAID Logical Volumes”.
The LVM metadata daemon, lvmetad, is supported in Red Hat Enterprise Linux release 6.4.
Enabling this daemon reduces the amount of scanning on systems with many block devices.
The lvmetad daemon is not currently supported across the nodes of a cluster, and requires that
the locking type be local file-based locking.
For information on the metadata daemon, see Section 4.6, “The Metadata Daemon (lvmetad)”.
In addition, small technical corrections and clarifications have been made throughout the document.
2.1.6. New and Changed Features for Red Hat Enterprise Linux 6.5
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Logical Volume Manager Administration
Red Hat Enterprise Linux 6.5 includes the following documentation and feature updates and changes.
You can control I/O operations on a RAID1 logical volume with the --writemostly and -writebehind parameters of the lvchange command. For information on these parameters,
see Section 5.4.16.11, “Controlling I/O Operations on a RAID1 Logical Volume”.
The lvchange command now supports a --refresh parameter that allows you to restore a
transiently failed device without having to reactivate the device. This feature is described in
Section 5.4.16.8.1, “The allocate RAID Fault Policy”.
LVM provides scrubbing support for RAID logical volumes. For information on this feature, see
Section 5.4.16.10, “Scrubbing a RAID Logical Volume”.
The fields that the lvs command supports have been updated. For information on the lvs
command, see Table 5.4, “lvs Display Fields”.
The lvchange command supports the new --maxrecoveryrate and --minrecoveryrate
parameters, which allow you to control the rate at which sync operations are performed. For
information on these parameters, see Section 5.4.16.10, “Scrubbing a RAID Logical Volume”.
You can control the rate at which a RAID logical volume is initialized by implementing recovery
throttling. You control the rate at which sync operations are performed by setting the minimum
and maximum I/O rate for those operations with the --minrecoveryrate and -maxrecoveryrate options of the lvcreate command, as described in Section 5.4.16.1,
“Creating a RAID Logical Volume”.
You can now create a thinly-provisioned snapshot of a non-thinly-provisioned logical volume.
For information on creating these volumes, known as external volumes, see Section 3.3.7,
“Thinly-Provisioned Snapshot Volumes”.
In addition, small technical corrections and clarifications have been made throughout the document.
2.1.7. New and Changed Features for Red Hat Enterprise Linux 6.6
Red Hat Enterprise Linux 6.6 includes the following documentation and feature updates and changes.
The documentation for thinly-provisioned volumes and thinly-provisioned snapshots has been
clarified. Additional information about LVM thin provisioning is now provided in the lvmthin(7)
man page. For general information on thinly-provisioned logical volumes, see Section 3.3.5,
“Thinly-Provisioned Logical Volumes (Thin Volumes)”. For information on thinly-provisioned
snapshot volumes, see Section 3.3.7, “Thinly-Provisioned Snapshot Volumes”.
This manual now documents the lvm dumpconfig command, in Section B.2, “The
lvmconfig Command”. Note that as of the Red Hat Enterprise Linux 6.8 release, this command
was renamed lvmconf, although the old format continues to work.
This manual now documents LVM profiles, in Section B.3, “LVM Profiles”.
This manual now documents the lvm command in Section 4.7, “Displaying LVM Information with
the lvm Command”.
In the Red Hat Enterprise Linux 6.6 release, you can control activation of thin pool snapshots
with the -k and -K options of the lvcreate and lvchange command, as documented in
Section 5.4.17, “Controlling Logical Volume Activation”.
This manual documents the --force argument of the vgimport command. This allows you to
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CHAPTER 2. THE LVM LOGICAL VOLUME MANAGER
import volume groups that are missing physical volumes and subsequently run the vgreduce -removemissing command. For information on the vgimport command, see Section 5.3.15,
“Moving a Volume Group to Another System”.
In addition, small technical corrections and clarifications have been made throughout the document.
2.1.8. New and Changed Features for Red Hat Enterprise Linux 6.7
Red Hat Enterprise Linux 6.7 includes the following documentation and feature updates and changes.
As of Red Hat Enterprise Linux release 6.7, many LVM processing commands accept the -S or
--select option to define selection criteria for those commands. LVM selection criteria are
documented in the new appendix Appendix C, LVM Selection Criteria.
This document provides basic procedures for creating cache logical volumes in Section 5.4.7,
“Creating LVM Cache Logical Volumes”.
The troubleshooting chapter of this document includes a new section, Section 7.8, “Duplicate PV
Warnings for Multipathed Devices”.
2.1.9. New and Changed Features for Red Hat Enterprise Linux 6.8
Red Hat Enterprise Linux 6.8 includes the following documentation and feature updates and changes.
When defining selection criteria for LVM commands, you can now specify time values as
selection criteria for fields with a field type of time. For information on specifying time values as
selection criteria, see Section C.3.1, “Specifying Time Values”.
2.2. LOGICAL VOLUMES
Volume management creates a layer of abstraction over physical storage, allowing you to create logical
storage volumes. This provides much greater flexibility in a number of ways than using physical storage
directly. With a logical volume, you are not restricted to physical disk sizes. In addition, the hardware
storage configuration is hidden from the software so it can be resized and moved without stopping
applications or unmounting file systems. This can reduce operational costs.
Logical volumes provide the following advantages over using physical storage directly:
Flexible capacity
When using logical volumes, file systems can extend across multiple disks, since you can
aggregate disks and partitions into a single logical volume.
Resizeable storage pools
You can extend logical volumes or reduce logical volumes in size with simple software
commands, without reformatting and repartitioning the underlying disk devices.
Online data relocation
To deploy newer, faster, or more resilient storage subsystems, you can move data while your
system is active. Data can be rearranged on disks while the disks are in use. For example, you
can empty a hot-swappable disk before removing it.
Convenient device naming
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Logical Volume Manager Administration
Logical storage volumes can be managed in user-defined groups, which you can name
according to your convenience.
Disk striping
You can create a logical volume that stripes data across two or more disks. This can
dramatically increase throughput.
Mirroring volumes
Logical volumes provide a convenient way to configure a mirror for your data.
Volume Snapshots
Using logical volumes, you can take device snapshots for consistent backups or to test the effect
of changes without affecting the real data.
The implementation of these features in LVM is described in the remainder of this document.
2.3. LVM ARCHITECTURE OVERVIEW
For the Red Hat Enterprise Linux 4 release of the Linux operating system, the original LVM1 logical
volume manager was replaced by LVM2, which has a more generic kernel framework than LVM1. LVM2
provides the following improvements over LVM1:
flexible capacity
more efficient metadata storage
better recovery format
new ASCII metadata format
atomic changes to metadata
redundant copies of metadata
LVM2 is backwards compatible with LVM1, with the exception of snapshot and cluster support. You can
convert a volume group from LVM1 format to LVM2 format with the vgconvert command. For
information on converting LVM metadata format, see the vgconvert(8) man page.
The underlying physical storage unit of an LVM logical volume is a block device such as a partition or
whole disk. This device is initialized as an LVM physical volume (PV).
To create an LVM logical volume, the physical volumes are combined into a volume group (VG). This
creates a pool of disk space out of which LVM logical volumes (LVs) can be allocated. This process is
analogous to the way in which disks are divided into partitions. A logical volume is used by file systems
and applications (such as databases).
Figure 2.1, “LVM Logical Volume Components” shows the components of a simple LVM logical volume:
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CHAPTER 2. THE LVM LOGICAL VOLUME MANAGER
Figure 2.1. LVM Logical Volume Components
For detailed information on the components of an LVM logical volume, see Chapter 3, LVM Components.
2.4. THE CLUSTERED LOGICAL VOLUME MANAGER (CLVM)
The Clustered Logical Volume Manager (CLVM) is a set of clustering extensions to LVM. These
extensions allow a cluster of computers to manage shared storage (for example, on a SAN) using LVM.
CLVM is part of the Resilient Storage Add-On.
Whether you should use CLVM depends on your system requirements:
If only one node of your system requires access to the storage you are configuring as logical
volumes, then you can use LVM without the CLVM extensions and the logical volumes created
with that node are all local to the node.
If you are using a clustered system for failover where only a single node that accesses the
storage is active at any one time, you should use High Availability Logical Volume Management
agents (HA-LVM).
If more than one node of your cluster will require access to your storage which is then shared
among the active nodes, then you must use CLVM. CLVM allows a user to configure logical
volumes on shared storage by locking access to physical storage while a logical volume is being
configured, and uses clustered locking services to manage the shared storage.
In order to use CLVM, the High Availability Add-On and Resilient Storage Add-On software, including the
clvmd daemon, must be running. The clvmd daemon is the key clustering extension to LVM. The
clvmd daemon runs in each cluster computer and distributes LVM metadata updates in a cluster,
presenting each cluster computer with the same view of the logical volumes. For information on installing
and administering the High Availability Add-On see Cluster Administration.
To ensure that clvmd is started at boot time, you can execute a chkconfig ... on command on the
clvmd service, as follows:
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# chkconfig clvmd on
If the clvmd daemon has not been started, you can execute a service ... start command on the
clvmd service, as follows:
# service clvmd start
Creating LVM logical volumes in a cluster environment is identical to creating LVM logical volumes on a
single node. There is no difference in the LVM commands themselves, or in the LVM graphical user
interface, as described in Chapter 5, LVM Administration with CLI Commands and Chapter 8, LVM
Administration with the LVM GUI. In order to enable the LVM volumes you are creating in a cluster, the
cluster infrastructure must be running and the cluster must be quorate.
By default, logical volumes created with CLVM on shared storage are visible to all systems that have
access to the shared storage. It is possible to create volume groups in which all of the storage devices
are visible to only one node in the cluster. It is also possible to change the status of a volume group from
a local volume group to a clustered volume group. For information, see Section 5.3.3, “Creating Volume
Groups in a Cluster” and Section 5.3.8, “Changing the Parameters of a Volume Group”.

WARNING
When you create volume groups with CLVM on shared storage, you must ensure
that all nodes in the cluster have access to the physical volumes that constitute the
volume group. Asymmetric cluster configurations in which some nodes have access
to the storage and others do not are not supported.
Figure 2.2, “CLVM Overview” shows a CLVM overview in a cluster.
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CHAPTER 2. THE LVM LOGICAL VOLUME MANAGER
Figure 2.2. CLVM Overview
NOTE
CLVM requires changes to the lvm.conf file for cluster-wide locking. Information on
configuring the lvm.conf file to support clustered locking is provided within the
lvm.conf file itself. For information about the lvm.conf file, see Appendix B, The LVM
Configuration Files.
2.5. DOCUMENT OVERVIEW
This remainder of this document includes the following chapters:
Chapter 3, LVM Components describes the components that make up an LVM logical volume.
Chapter 4, LVM Administration Overview provides an overview of the basic steps you perform to
configure LVM logical volumes, whether you are using the LVM Command Line Interface (CLI)
commands or the LVM Graphical User Interface (GUI).
Chapter 5, LVM Administration with CLI Commands summarizes the individual administrative
tasks you can perform with the LVM CLI commands to create and maintain logical volumes.
Chapter 6, LVM Configuration Examples provides a variety of LVM configuration examples.
Chapter 7, LVM Troubleshooting provides instructions for troubleshooting a variety of LVM
issues.
Chapter 8, LVM Administration with the LVM GUI summarizes the operating of the LVM GUI.
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Appendix A, The Device Mapper describes the Device Mapper that LVM uses to map logical and
physical volumes.
Appendix B, The LVM Configuration Files describes the LVM configuration files.
Appendix D, LVM Object Tags describes LVM object tags and host tags.
Appendix E, LVM Volume Group Metadata describes LVM volume group metadata, and includes
a sample copy of metadata for an LVM volume group.
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CHAPTER 3. LVM COMPONENTS
CHAPTER 3. LVM COMPONENTS
This chapter describes the components of an LVM Logical volume.
3.1. PHYSICAL VOLUMES
The underlying physical storage unit of an LVM logical volume is a block device such as a partition or
whole disk. To use the device for an LVM logical volume the device must be initialized as a physical
volume (PV). Initializing a block device as a physical volume places a label near the start of the device.
By default, the LVM label is placed in the second 512-byte sector. You can overwrite this default by
placing the label on any of the first 4 sectors. This allows LVM volumes to co-exist with other users of
these sectors, if necessary.
An LVM label provides correct identification and device ordering for a physical device, since devices can
come up in any order when the system is booted. An LVM label remains persistent across reboots and
throughout a cluster.
The LVM label identifies the device as an LVM physical volume. It contains a random unique identifier
(the UUID) for the physical volume. It also stores the size of the block device in bytes, and it records
where the LVM metadata will be stored on the device.
The LVM metadata contains the configuration details of the LVM volume groups on your system. By
default, an identical copy of the metadata is maintained in every metadata area in every physical volume
within the volume group. LVM metadata is small and stored as ASCII.
Currently LVM allows you to store 0, 1 or 2 identical copies of its metadata on each physical volume.
The default is 1 copy. Once you configure the number of metadata copies on the physical volume, you
cannot change that number at a later time. The first copy is stored at the start of the device, shortly after
the label. If there is a second copy, it is placed at the end of the device. If you accidentally overwrite the
area at the beginning of your disk by writing to a different disk than you intend, a second copy of the
metadata at the end of the device will allow you to recover the metadata.
For detailed information about the LVM metadata and changing the metadata parameters, see
Appendix E, LVM Volume Group Metadata.
3.1.1. LVM Physical Volume Layout
Figure 3.1, “Physical Volume layout” shows the layout of an LVM physical volume. The LVM label is on
the second sector, followed by the metadata area, followed by the usable space on the device.
NOTE
In the Linux kernel (and throughout this document), sectors are considered to be 512
bytes in size.
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Logical Volume Manager Administration
Figure 3.1. Physical Volume layout
3.1.2. Multiple Partitions on a Disk
LVM allows you to create physical volumes out of disk partitions. It is generally recommended that you
create a single partition that covers the whole disk to label as an LVM physical volume for the following
reasons:
Administrative convenience
It is easier to keep track of the hardware in a system if each real disk only appears once. This
becomes particularly true if a disk fails. In addition, multiple physical volumes on a single disk
may cause a kernel warning about unknown partition types at boot-up.
Striping performance
LVM cannot tell that two physical volumes are on the same physical disk. If you create a striped
logical volume when two physical volumes are on the same physical disk, the stripes could be on
different partitions on the same disk. This would result in a decrease in performance rather than
an increase.
Although it is not recommended, there may be specific circumstances when you will need to divide a disk
into separate LVM physical volumes. For example, on a system with few disks it may be necessary to
move data around partitions when you are migrating an existing system to LVM volumes. Additionally, if
you have a very large disk and want to have more than one volume group for administrative purposes
then it is necessary to partition the disk. If you do have a disk with more than one partition and both of
those partitions are in the same volume group, take care to specify which partitions are to be included in
a logical volume when creating striped volumes.
3.2. VOLUME GROUPS
Physical volumes are combined into volume groups (VGs). This creates a pool of disk space out of
which logical volumes can be allocated.
Within a volume group, the disk space available for allocation is divided into units of a fixed-size called
extents. An extent is the smallest unit of space that can be allocated. Within a physical volume, extents
are referred to as physical extents.
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CHAPTER 3. LVM COMPONENTS
A logical volume is allocated into logical extents of the same size as the physical extents. The extent size
is thus the same for all logical volumes in the volume group. The volume group maps the logical extents
to physical extents.
3.3. LVM LOGICAL VOLUMES
In LVM, a volume group is divided up into logical volumes. There are three types of LVM logical volumes:
linear volumes, striped volumes, and mirrored volumes. These are described in the following sections.
3.3.1. Linear Volumes
A linear volume aggregates space from one or more physical volumes into one logical volume. For
example, if you have two 60GB disks, you can create a 120GB logical volume. The physical storage is
concatenated.
Creating a linear volume assigns a range of physical extents to an area of a logical volume in order. For
example, as shown in Figure 3.2, “Extent Mapping” logical extents 1 to 99 could map to one physical
volume and logical extents 100 to 198 could map to a second physical volume. From the point of view of
the application, there is one device that is 198 extents in size.
Figure 3.2. Extent Mapping
The physical volumes that make up a logical volume do not have to be the same size. Figure 3.3, “Linear
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Volume with Unequal Physical Volumes” shows volume group VG1 with a physical extent size of 4MB.
This volume group includes 2 physical volumes named PV1 and PV2. The physical volumes are divided
into 4MB units, since that is the extent size. In this example, PV1 is 200 extents in size (800MB) and PV2
is 100 extents in size (400MB). You can create a linear volume any size between 1 and 300 extents
(4MB to 1200MB). In this example, the linear volume named LV1 is 300 extents in size.
Figure 3.3. Linear Volume with Unequal Physical Volumes
You can configure more than one linear logical volume of whatever size you require from the pool of
physical extents. Figure 3.4, “Multiple Logical Volumes” shows the same volume group as in Figure 3.3,
“Linear Volume with Unequal Physical Volumes”, but in this case two logical volumes have been carved
out of the volume group: LV1, which is 250 extents in size (1000MB) and LV2 which is 50 extents in size
(200MB).
Figure 3.4. Multiple Logical Volumes
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CHAPTER 3. LVM COMPONENTS
3.3.2. Striped Logical Volumes
When you write data to an LVM logical volume, the file system lays the data out across the underlying
physical volumes. You can control the way the data is written to the physical volumes by creating a
striped logical volume. For large sequential reads and writes, this can improve the efficiency of the data
I/O.
Striping enhances performance by writing data to a predetermined number of physical volumes in roundrobin fashion. With striping, I/O can be done in parallel. In some situations, this can result in near-linear
performance gain for each additional physical volume in the stripe.
The following illustration shows data being striped across three physical volumes. In this figure:
the first stripe of data is written to PV1
the second stripe of data is written to PV2
the third stripe of data is written to PV3
the fourth stripe of data is written to PV1
In a striped logical volume, the size of the stripe cannot exceed the size of an extent.
Figure 3.5. Striping Data Across Three PVs
Striped logical volumes can be extended by concatenating another set of devices onto the end of the first
set. In order to extend a striped logical volume, however, there must be enough free space on the
underlying physical volumes that make up the volume group to support the stripe. For example, if you
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have a two-way stripe that uses up an entire volume group, adding a single physical volume to the
volume group will not enable you to extend the stripe. Instead, you must add at least two physical
volumes to the volume group. For more information on extending a striped volume, see Section 5.4.14.1,
“Extending a Striped Volume”.
3.3.3. Mirrored Logical Volumes
A mirror maintains identical copies of data on different devices. When data is written to one device, it is
written to a second device as well, mirroring the data. This provides protection for device failures. When
one leg of a mirror fails, the logical volume becomes a linear volume and can still be accessed.
LVM supports mirrored volumes. When you create a mirrored logical volume, LVM ensures that data
written to an underlying physical volume is mirrored onto a separate physical volume. With LVM, you can
create mirrored logical volumes with multiple mirrors.
An LVM mirror divides the device being copied into regions that are typically 512KB in size. LVM
maintains a small log which it uses to keep track of which regions are in sync with the mirror or mirrors.
This log can be kept on disk, which will keep it persistent across reboots, or it can be maintained in
memory.
Figure 3.6, “Mirrored Logical Volume” shows a mirrored logical volume with one mirror. In this
configuration, the log is maintained on disk.
Figure 3.6. Mirrored Logical Volume
For information on creating and modifying mirrors, see Section 5.4.3, “Creating Mirrored Volumes”.
3.3.4. RAID Logical Volumes
As of the Red Hat Enterprise Linux 6.3 release, LVM supports RAID logical volumes. For information on
the RAID implementations that LVM supports, see Section 5.4.16, “RAID Logical Volumes”.
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CHAPTER 3. LVM COMPONENTS
3.3.5. Thinly-Provisioned Logical Volumes (Thin Volumes)
As of the Red Hat Enterprise Linux 6.4 release, logical volumes can be thinly provisioned. This allows
you to create logical volumes that are larger than the available extents. Using thin provisioning, you can
manage a storage pool of free space, known as a thin pool, which can be allocated to an arbitrary
number of devices when needed by applications. You can then create devices that can be bound to the
thin pool for later allocation when an application actually writes to the logical volume. The thin pool can
be expanded dynamically when needed for cost-effective allocation of storage space.
NOTE
Thin volumes are not supported across the nodes in a cluster. The thin pool and all its thin
volumes must be exclusively activated on only one cluster node.
By using thin provisioning, a storage administrator can over-commit the physical storage, often avoiding
the need to purchase additional storage. For example, if ten users each request a 100GB file system for
their application, the storage administrator can create what appears to be a 100GB file system for each
user but which is backed by less actual storage that is used only when needed. When using thin
provisioning, it is important that the storage administrator monitor the storage pool and add more
capacity if it starts to become full.
To make sure that all available space can be used, LVM supports data discard. This allows for re-use of
the space that was formerly used by a discarded file or other block range.
For information on creating thin volumes, see Section 5.4.4, “Creating Thinly-Provisioned Logical
Volumes”.
Thin volumes provide support for a new implementation of copy-on-write (COW) snapshot logical
volumes, which allow many virtual devices to share the same data in the thin pool. For information on
thin snapshot volumes, see Section 3.3.7, “Thinly-Provisioned Snapshot Volumes”.
3.3.6. Snapshot Volumes
The LVM snapshot feature provides the ability to create virtual images of a device at a particular instant
without causing a service interruption. When a change is made to the original device (the origin) after a
snapshot is taken, the snapshot feature makes a copy of the changed data area as it was prior to the
change so that it can reconstruct the state of the device.
NOTE
As of the Red Hat Enterprise Linux 6.4 release, LVM supports thinly-provisioned
snapshots. For information on thinly provisioned snapshot volumes, see Section 3.3.7,
“Thinly-Provisioned Snapshot Volumes”.
NOTE
LVM snapshots are not supported across the nodes in a cluster. You cannot create a
snapshot volume in a clustered volume group.
Because a snapshot copies only the data areas that change after the snapshot is created, the snapshot
feature requires a minimal amount of storage. For example, with a rarely updated origin, 3-5 % of the
origin's capacity is sufficient to maintain the snapshot.
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Logical Volume Manager Administration
NOTE
Snapshot copies of a file system are virtual copies, not actual media backup for a file
system. Snapshots do not provide a substitute for a backup procedure.
The size of the snapshot governs the amount of space set aside for storing the changes to the origin
volume. For example, if you made a snapshot and then completely overwrote the origin the snapshot
would have to be at least as big as the origin volume to hold the changes. You need to dimension a
snapshot according to the expected level of change. So for example a short-lived snapshot of a readmostly volume, such as /usr, would need less space than a long-lived snapshot of a volume that sees a
greater number of writes, such as /home.
If a snapshot runs full, the snapshot becomes invalid, since it can no longer track changes on the origin
volume. You should regularly monitor the size of the snapshot. Snapshots are fully resizeable, however,
so if you have the storage capacity you can increase the size of the snapshot volume to prevent it from
getting dropped. Conversely, if you find that the snapshot volume is larger than you need, you can
reduce the size of the volume to free up space that is needed by other logical volumes.
When you create a snapshot file system, full read and write access to the origin stays possible. If a
chunk on a snapshot is changed, that chunk is marked and never gets copied from the original volume.
There are several uses for the snapshot feature:
Most typically, a snapshot is taken when you need to perform a backup on a logical volume
without halting the live system that is continuously updating the data.
You can execute the fsck command on a snapshot file system to check the file system integrity
and determine whether the original file system requires file system repair.
Because the snapshot is read/write, you can test applications against production data by taking
a snapshot and running tests against the snapshot, leaving the real data untouched.
You can create LVM volumes for use with Red Hat virtualization. LVM snapshots can be used to
create snapshots of virtual guest images. These snapshots can provide a convenient way to
modify existing guests or create new guests with minimal additional storage. For information on
creating LVM-based storage pools with Red Hat Virtualization, see the Virtualization
Administration Guide.
For information on creating snapshot volumes, see Section 5.4.5, “Creating Snapshot Volumes”.
As of the Red Hat Enterprise Linux 6 release, you can use the --merge option of the lvconvert
command to merge a snapshot into its origin volume. One use for this feature is to perform system
rollback if you have lost data or files or otherwise need to restore your system to a previous state. After
you merge the snapshot volume, the resulting logical volume will have the origin volume's name, minor
number, and UUID and the merged snapshot is removed. For information on using this option, see
Section 5.4.8, “Merging Snapshot Volumes”.
3.3.7. Thinly-Provisioned Snapshot Volumes
The Red Hat Enterprise Linux release 6.4 version of LVM provides support for thinly-provisioned
snapshot volumes. Thin snapshot volumes allow many virtual devices to be stored on the same data
volume. This simplifies administration and allows for the sharing of data between snapshot volumes.
As for all LVM snapshot volumes, as well as all thin volumes, thin snapshot volumes are not supported
across the nodes in a cluster. The snapshot volume must be exclusively activated on only one cluster
node.
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CHAPTER 3. LVM COMPONENTS
Thin snapshot volumes provide the following benefits:
A thin snapshot volume can reduce disk usage when there are multiple snapshots of the same
origin volume.
If there are multiple snapshots of the same origin, then a write to the origin will cause one COW
operation to preserve the data. Increasing the number of snapshots of the origin should yield no
major slowdown.
Thin snapshot volumes can be used as a logical volume origin for another snapshot. This allows
for an arbitrary depth of recursive snapshots (snapshots of snapshots of snapshots...).
A snapshot of a thin logical volume also creates a thin logical volume. This consumes no data
space until a COW operation is required, or until the snapshot itself is written.
A thin snapshot volume does not need to be activated with its origin, so a user may have only
the origin active while there are many inactive snapshot volumes of the origin.
When you delete the origin of a thinly-provisioned snapshot volume, each snapshot of that origin
volume becomes an independent thinly-provisioned volume. This means that instead of merging
a snapshot with its origin volume, you may choose to delete the origin volume and then create a
new thinly-provisioned snapshot using that independent volume as the origin volume for the new
snapshot.
Although there are many advantages to using thin snapshot volumes, there are some use cases for
which the older LVM snapshot volume feature may be more appropriate to your needs:
You cannot change the chunk size of a thin pool. If the thin pool has a large chunk size (for
example, 1MB) and you require a short-living snapshot for which a chunk size that large is not
efficient, you may elect to use the older snapshot feature.
You cannot limit the size of a thin snapshot volume; the snapshot will use all of the space in the
thin pool, if necessary. This may not be appropriate for your needs.
In general, you should consider the specific requirements of your site when deciding which snapshot
format to use.
For information on configuring thin snapshot volumes, see Section 5.4.6, “Creating Thinly-Provisioned
Snapshot Volumes”.
3.3.8. Cache Volumes
As of the Red Hat Enterprise Linux 6.7 release, LVM supports the use of fast block devices (such as
SSD drives) as write-back or write-though caches for larger slower block devices. Users can create
cache logical volumes to improve the performance of their existing logical volumes or create new cache
logical volumes composed of a small and fast device coupled with a large and slow device.
For information on creating LVM cache volumes, see Section 5.4.7, “Creating LVM Cache Logical
Volumes”.
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Logical Volume Manager Administration
CHAPTER 4. LVM ADMINISTRATION OVERVIEW
This chapter provides an overview of the administrative procedures you use to configure LVM logical
volumes. This chapter is intended to provide a general understanding of the steps involved. For specific
step-by-step examples of common LVM configuration procedures, see Chapter 6, LVM Configuration
Examples.
For descriptions of the CLI commands you can use to perform LVM administration, see Chapter 5, LVM
Administration with CLI Commands. Alternately, you can use the LVM GUI, which is described in
Chapter 8, LVM Administration with the LVM GUI .
4.1. CREATING LVM VOLUMES IN A CLUSTER
To create logical volumes in a cluster environment, you use the Clustered Logical Volume Manager
(CLVM), which is a set of clustering extensions to LVM. These extensions allow a cluster of computers to
manage shared storage (for example, on a SAN) using LVM. In order to use CLVM, the High Availability
Add-On and Resilient Storage Add-On software, including the clvmd daemon, must be started at boot
time, as described in Section 2.4, “The Clustered Logical Volume Manager (CLVM)”.
Creating LVM logical volumes in a cluster environment is identical to creating LVM logical volumes on a
single node. There is no difference in the LVM commands themselves, or in the LVM GUI interface. In
order to enable the LVM volumes you are creating in a cluster, the cluster infrastructure must be running
and the cluster must be quorate.
CLVM requires changes to the lvm.conf file for cluster-wide locking. Information on configuring the
lvm.conf file to support clustered locking is provided within the lvm.conf file itself. For information
about the lvm.conf file, see Appendix B, The LVM Configuration Files.
By default, logical volumes created with CLVM on shared storage are visible to all systems that have
access to the shared storage. It is possible to create volume groups in which all of the storage devices
are visible to only one node in the cluster. It is also possible to change the status of a volume group from
a local volume group to a clustered volume group. For information, see Section 5.3.3, “Creating Volume
Groups in a Cluster” and Section 5.3.8, “Changing the Parameters of a Volume Group”

WARNING
When you create volume groups with CLVM on shared storage, you must ensure
that all nodes in the cluster have access to the physical volumes that constitute the
volume group. Asymmetric cluster configurations in which some nodes have access
to the storage and others do not are not supported.
For information on how to install the High Availability Add-On and set up the cluster infrastructure, see
Cluster Administration.
For an example of creating a mirrored logical volume in a cluster, see Section 6.5, “Creating a Mirrored
LVM Logical Volume in a Cluster”.
4.2. LOGICAL VOLUME CREATION OVERVIEW
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CHAPTER 4. LVM ADMINISTRATION OVERVIEW
The following is a summary of the steps to perform to create an LVM logical volume.
1. Initialize the partitions you will use for the LVM volume as physical volumes (this labels them).
2. Create a volume group.
3. Create a logical volume.
After creating the logical volume you can create and mount the file system. The examples in this
document use GFS2 file systems.
NOTE
Although a GFS2 file system can be implemented in a standalone system or as part of a
cluster configuration, for the Red Hat Enterprise Linux 6 release Red Hat does not support
the use of GFS2 as a single-node file system. Red Hat will continue to support singlenode GFS2 file systems for mounting snapshots of cluster file systems (for example, for
backup purposes).
1. Create a GFS2 file system on the logical volume with the mkfs.gfs2 command.
2. Create a new mount point with the mkdir command. In a clustered system, create the mount
point on all nodes in the cluster.
3. Mount the file system. You may want to add a line to the fstab file for each node in the system.
Alternately, you can create and mount the GFS2 file system with the LVM GUI.
Creating the LVM volume is machine independent, since the storage area for LVM setup information is
on the physical volumes and not the machine where the volume was created. Servers that use the
storage have local copies, but can recreate that from what is on the physical volumes. You can attach
physical volumes to a different server if the LVM versions are compatible.
4.3. GROWING A FILE SYSTEM ON A LOGICAL VOLUME
To grow a file system on a logical volume, perform the following steps:
1. Make a new physical volume.
2. Extend the volume group that contains the logical volume with the file system you are growing to
include the new physical volume.
3. Extend the logical volume to include the new physical volume.
4. Grow the file system.
If you have sufficient unallocated space in the volume group, you can use that space to extend the logical
volume instead of performing steps 1 and 2.
4.4. LOGICAL VOLUME BACKUP
Metadata backups and archives are automatically created on every volume group and logical volume
configuration change unless disabled in the lvm.conf file. By default, the metadata backup is stored in
the /etc/lvm/backup file and the metadata archives are stored in the /etc/lvm/archive file. How
29
Logical Volume Manager Administration
long the metadata archives stored in the /etc/lvm/archive file are kept and how many archive files
are kept is determined by parameters you can set in the lvm.conf file. A daily system backup should
include the contents of the /etc/lvm directory in the backup.
Note that a metadata backup does not back up the user and system data contained in the logical
volumes.
You can manually back up the metadata to the /etc/lvm/backup file with the vgcfgbackup
command. You can restore metadata with the vgcfgrestore command. The vgcfgbackup and
vgcfgrestore commands are described in Section 5.3.13, “Backing Up Volume Group Metadata”.
4.5. LOGGING
All message output passes through a logging module with independent choices of logging levels for:
standard output/error
syslog
log file
external log function
The logging levels are set in the /etc/lvm/lvm.conf file, which is described in Appendix B, The LVM
Configuration Files.
4.6. THE METADATA DAEMON (LVMETAD)
LVM can optionally use a central metadata cache, implemented through a daemon (lvmetad) and a
udev rule. The metadata daemon has two main purposes: It improves performance of LVM commands
and it allows udev to automatically activate logical volumes or entire volume groups as they become
available to the system.
NOTE
The lvmetad daemon is not currently supported across the nodes of a cluster, and
requires that the locking type be local file-based locking.
To take advantage of the daemon, you must do the following:
Start the daemon through the lvm2-lvmetad service. To start the daemon automatically at boot
time, use the chkconfig lvm2-lvmetad on command. To start the daemon manually, use
the service lvm2-lvmetad start command.
Configure LVM to make use of the daemon by setting the global/use_lvmetad variable to 1
in the lvm.conf configuration file. For information on the lvm.conf configuration file, see
Appendix B, The LVM Configuration Files.
Normally, each LVM command issues a disk scan to find all relevant physical volumes and to read
volume group metadata. However, if the metadata daemon is running and enabled, this expensive scan
can be skipped. Instead, the lvmetad daemon scans each device only once, when it becomes
available, by means of udev rules. This can save a significant amount of I/O and reduce the time
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CHAPTER 4. LVM ADMINISTRATION OVERVIEW
required to complete LVM operations, particularly on systems with many disks. For information on the
udev device manager and udev rules, see Section A.3, “Device Mapper Support for the udev Device
Manager”.
When a new volume group is made available at runtime (for example, through hotplug or iSCSI), its
logical volumes must be activated in order to be used. When the lvmetad daemon is enabled, the
activation/auto_activation_volume_list option in the lvm.conf configuration file can be
used to configure a list of volume groups and logical volumes that should be automatically activated.
Without the lvmetad daemon, a manual activation is necessary. By default, this list is not defined, which
means that all volumes are autoactivated once all of the physical volumes are in place. The
autoactivation works recursively for LVM stacked on top of other devices, as it is event-based.
NOTE
When the lvmetad daemon is running, the filter = setting in the
/etc/lvm/lvm.conf file does not apply when you execute the pvscan --cache
device command. To filter devices, you need to use the global_filter = setting.
Devices that fail the global filter are not opened by LVM and are never scanned. You may
need to use a global filter, for example, when you use LVM devices in VMs and you do
not want the contents of the devices in the VMs to be scanned by the physical host.
4.7. DISPLAYING LVM INFORMATION WITH THE LVM COMMAND
The lvm command provides several built-in options that you can use to display information about LVM
support and configuration.
lvm devtypes
Displays the recognized built-in block device types (Red Hat Enterprise Linux release 6.6 and
later).
lvm formats
Displays recognizes metadata formats.
lvm help
Displays LVM help text.
lvm segtypes
Displays recognized logical volume segment types.
lvm tags
Displays any tags defined on this host. For information on LVM object tags, see Appendix D,
LVM Object Tags.
lvm version
Displays the current version information.
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Logical Volume Manager Administration
CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
This chapter summarizes the individual administrative tasks you can perform with the LVM Command
Line Interface (CLI) commands to create and maintain logical volumes.
NOTE
If you are creating or modifying an LVM volume for a clustered environment, you must
ensure that you are running the clvmd daemon. For information, see Section 4.1,
“Creating LVM Volumes in a Cluster”.
5.1. USING CLI COMMANDS
There are several general features of all LVM CLI commands.
When sizes are required in a command line argument, units can always be specified explicitly. If you do
not specify a unit, then a default is assumed, usually KB or MB. LVM CLI commands do not accept
fractions.
When specifying units in a command line argument, LVM is case-insensitive; specifying M or m is
equivalent, for example, and powers of 2 (multiples of 1024) are used. However, when specifying the -units argument in a command, lower-case indicates that units are in multiples of 1024 while upper-case
indicates that units are in multiples of 1000.
Where commands take volume group or logical volume names as arguments, the full path name is
optional. A logical volume called lvol0 in a volume group called vg0 can be specified as vg0/lvol0.
Where a list of volume groups is required but is left empty, a list of all volume groups will be substituted.
Where a list of logical volumes is required but a volume group is given, a list of all the logical volumes in
that volume group will be substituted. For example, the lvdisplay vg0 command will display all the
logical volumes in volume group vg0.
All LVM commands accept a -v argument, which can be entered multiple times to increase the output
verbosity. For example, the following examples shows the default output of the lvcreate command.
# lvcreate -L 50MB new_vg
Rounding up size to full physical extent 52.00 MB
Logical volume "lvol0" created
The following command shows the output of the lvcreate command with the -v argument.
# lvcreate -v -L 50MB new_vg
Finding volume group "new_vg"
Rounding up size to full physical extent 52.00 MB
Archiving volume group "new_vg" metadata (seqno 4).
Creating logical volume lvol0
Creating volume group backup "/etc/lvm/backup/new_vg" (seqno 5).
Found volume group "new_vg"
Creating new_vg-lvol0
Loading new_vg-lvol0 table
Resuming new_vg-lvol0 (253:2)
Clearing start of logical volume "lvol0"
Creating volume group backup "/etc/lvm/backup/new_vg" (seqno 5).
Logical volume "lvol0" created
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
You could also have used the -vv, -vvv or the -vvvv argument to display increasingly more details
about the command execution. The -vvvv argument provides the maximum amount of information at
this time. The following example shows only the first few lines of output for the lvcreate command
with the -vvvv argument specified.
# lvcreate -vvvv -L 50MB new_vg
#lvmcmdline.c:913
Processing: lvcreate -vvvv -L 50MB new_vg
#lvmcmdline.c:916
O_DIRECT will be used
#config/config.c:864
Setting global/locking_type to 1
#locking/locking.c:138
File-based locking selected.
#config/config.c:841
Setting global/locking_dir to /var/lock/lvm
#activate/activate.c:358
Getting target version for linear
#ioctl/libdm-iface.c:1569
dm version
OF
[16384]
#ioctl/libdm-iface.c:1569
dm versions
OF
[16384]
#activate/activate.c:358
Getting target version for striped
#ioctl/libdm-iface.c:1569
dm versions
OF
[16384]
#config/config.c:864
Setting activation/mirror_region_size to 512
...
You can display help for any of the LVM CLI commands with the --help argument of the command.
# commandname --help
To display the man page for a command, execute the man command:
# man commandname
The man lvm command provides general online information about LVM.
All LVM objects are referenced internally by a UUID, which is assigned when you create the object. This
can be useful in a situation where you remove a physical volume called /dev/sdf which is part of a
volume group and, when you plug it back in, you find that it is now /dev/sdk. LVM will still find the
physical volume because it identifies the physical volume by its UUID and not its device name. For
information on specifying the UUID of a physical volume when creating a physical volume, see
Section 7.4, “Recovering Physical Volume Metadata”.
5.2. PHYSICAL VOLUME ADMINISTRATION
This section describes the commands that perform the various aspects of physical volume
administration.
5.2.1. Creating Physical Volumes
The following subsections describe the commands used for creating physical volumes.
5.2.1.1. Setting the Partition Type
If you are using a whole disk device for your physical volume, the disk must have no partition table. For
DOS disk partitions, the partition id should be set to 0x8e using the fdisk or cfdisk command or an
equivalent. For whole disk devices only the partition table must be erased, which will effectively destroy
all data on that disk. You can remove an existing partition table by zeroing the first sector with the
following command:
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Logical Volume Manager Administration
# dd if=/dev/zero of=PhysicalVolume bs=512 count=1
5.2.1.2. Initializing Physical Volumes
Use the pvcreate command to initialize a block device to be used as a physical volume. Initialization is
analogous to formatting a file system.
The following command initializes /dev/sdd, /dev/sde, and /dev/sdf as LVM physical volumes for
later use as part of LVM logical volumes.
# pvcreate /dev/sdd /dev/sde /dev/sdf
To initialize partitions rather than whole disks: run the pvcreate command on the partition. The
following example initializes the partition /dev/hdb1 as an LVM physical volume for later use as part of
an LVM logical volume.
# pvcreate /dev/hdb1
5.2.1.3. Scanning for Block Devices
You can scan for block devices that may be used as physical volumes with the lvmdiskscan
command, as shown in the following example.
# lvmdiskscan
/dev/ram0
/dev/sda
/dev/root
/dev/ram
/dev/sda1
/dev/VolGroup00/LogVol01
/dev/ram2
/dev/new_vg/lvol0
/dev/ram3
/dev/pkl_new_vg/sparkie_lv
/dev/ram4
/dev/ram5
/dev/ram6
/dev/ram7
/dev/ram8
/dev/ram9
/dev/ram10
/dev/ram11
/dev/ram12
/dev/ram13
/dev/ram14
/dev/ram15
/dev/sdb
/dev/sdb1
/dev/sdc
/dev/sdc1
/dev/sdd
/dev/sdd1
7 disks
34
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
16.00
17.15
13.69
16.00
17.14
512.00
16.00
52.00
16.00
7.14
16.00
16.00
16.00
16.00
16.00
16.00
16.00
16.00
16.00
16.00
16.00
16.00
17.15
17.14
17.15
17.14
17.15
17.14
MB]
GB]
GB]
MB]
GB]
MB]
MB]
MB]
MB]
GB]
MB]
MB]
MB]
MB]
MB]
MB]
MB]
MB]
MB]
MB]
MB]
MB]
GB]
GB]
GB]
GB]
GB]
GB]
LVM physical volume
LVM physical volume
LVM physical volume
LVM physical volume
CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
17 partitions
0 LVM physical volume whole disks
4 LVM physical volumes
5.2.2. Displaying Physical Volumes
There are three commands you can use to display properties of LVM physical volumes: pvs,
pvdisplay, and pvscan.
The pvs command provides physical volume information in a configurable form, displaying one line per
physical volume. The pvs command provides a great deal of format control, and is useful for scripting.
For information on using the pvs command to customize your output, see Section 5.8, “Customized
Reporting for LVM”.
The pvdisplay command provides a verbose multi-line output for each physical volume. It displays
physical properties (size, extents, volume group, and so on) in a fixed format.
The following example shows the output of the pvdisplay command for a single physical volume.
# pvdisplay
--- Physical volume --PV Name
/dev/sdc1
VG Name
new_vg
PV Size
17.14 GB / not usable 3.40 MB
Allocatable
yes
PE Size (KByte)
4096
Total PE
4388
Free PE
4375
Allocated PE
13
PV UUID
Joqlch-yWSj-kuEn-IdwM-01S9-XO8M-mcpsVe
The pvscan command scans all supported LVM block devices in the system for physical volumes.
The following command shows all physical devices found:
# pvscan
PV /dev/sdb2
VG vg0
PV /dev/sdc1
VG vg0
PV /dev/sdc2
Total: 3 [2.83 GB] / in
lvm2
lvm2
lvm2
use:
[964.00
[964.00
[964.84
2 [1.88
MB / 0
free]
MB / 428.00 MB free]
MB]
GB] / in no VG: 1 [964.84 MB]
You can define a filter in the /etc/lvm/lvm.conf file so that this command will avoid scanning
specific physical volumes. For information on using filters to control which devices are scanned, see
Section 5.5, “Controlling LVM Device Scans with Filters” .
5.2.3. Preventing Allocation on a Physical Volume
You can prevent allocation of physical extents on the free space of one or more physical volumes with
the pvchange command. This may be necessary if there are disk errors, or if you will be removing the
physical volume.
The following command disallows the allocation of physical extents on /dev/sdk1.
# pvchange -x n /dev/sdk1
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Logical Volume Manager Administration
You can also use the -xy arguments of the pvchange command to allow allocation where it had
previously been disallowed.
5.2.4. Resizing a Physical Volume
If you need to change the size of an underlying block device for any reason, use the pvresize
command to update LVM with the new size. You can execute this command while LVM is using the
physical volume.
5.2.5. Removing Physical Volumes
If a device is no longer required for use by LVM, you can remove the LVM label with the pvremove
command. Executing the pvremove command zeroes the LVM metadata on an empty physical volume.
If the physical volume you want to remove is currently part of a volume group, you must remove it from
the volume group with the vgreduce command, as described in Section 5.3.7, “Removing Physical
Volumes from a Volume Group”.
# pvremove /dev/ram15
Labels on physical volume "/dev/ram15" successfully wiped
5.3. VOLUME GROUP ADMINISTRATION
This section describes the commands that perform the various aspects of volume group administration.
5.3.1. Creating Volume Groups
To create a volume group from one or more physical volumes, use the vgcreate command. The
vgcreate command creates a new volume group by name and adds at least one physical volume to it.
The following command creates a volume group named vg1 that contains physical volumes /dev/sdd1
and /dev/sde1.
# vgcreate vg1 /dev/sdd1 /dev/sde1
When physical volumes are used to create a volume group, its disk space is divided into 4MB extents,
by default. This extent is the minimum amount by which the logical volume may be increased or
decreased in size. Large numbers of extents will have no impact on I/O performance of the logical
volume.
You can specify the extent size with the -s option to the vgcreate command if the default extent size
is not suitable. You can put limits on the number of physical or logical volumes the volume group can
have by using the -p and -l arguments of the vgcreate command.
By default, a volume group allocates physical extents according to common-sense rules such as not
placing parallel stripes on the same physical volume. This is the normal allocation policy. You can use
the --alloc argument of the vgcreate command to specify an allocation policy of contiguous,
anywhere, or cling. In general, allocation policies other than normal are required only in special
cases where you need to specify unusual or nonstandard extent allocation. For further information on
how LVM allocates physical extents, see Section 5.3.2, “LVM Allocation”.
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
LVM volume groups and underlying logical volumes are included in the device special file directory tree
in the /dev directory with the following layout:
/dev/vg/lv/
For example, if you create two volume groups myvg1 and myvg2, each with three logical volumes
named lv01, lv02, and lv03, six device special files are created:
/dev/myvg1/lv01
/dev/myvg1/lv02
/dev/myvg1/lv03
/dev/myvg2/lv01
/dev/myvg2/lv02
/dev/myvg2/lv03
The device special files are not present if the corresponding logical volume is not currently active.
The maximum device size with LVM is 8 Exabytes on 64-bit CPUs.
5.3.2. LVM Allocation
When an LVM operation needs to allocate physical extents for one or more logical volumes, the
allocation proceeds as follows:
The complete set of unallocated physical extents in the volume group is generated for
consideration. If you supply any ranges of physical extents at the end of the command line, only
unallocated physical extents within those ranges on the specified physical volumes are
considered.
Each allocation policy is tried in turn, starting with the strictest policy (contiguous) and ending
with the allocation policy specified using the --alloc option or set as the default for the
particular logical volume or volume group. For each policy, working from the lowest-numbered
logical extent of the empty logical volume space that needs to be filled, as much space as
possible is allocated, according to the restrictions imposed by the allocation policy. If more space
is needed, LVM moves on to the next policy.
The allocation policy restrictions are as follows:
An allocation policy of contiguous requires that the physical location of any logical extent that
is not the first logical extent of a logical volume is adjacent to the physical location of the logical
extent immediately preceding it.
When a logical volume is striped or mirrored, the contiguous allocation restriction is applied
independently to each stripe or mirror image (leg) that needs space.
An allocation policy of cling requires that the physical volume used for any logical extent to be
added to an existing logical volume is already in use by at least one logical extent earlier in that
logical volume. If the configuration parameter allocation/cling_tag_list is defined, then
two physical volumes are considered to match if any of the listed tags is present on both
physical volumes. This allows groups of physical volumes with similar properties (such as their
physical location) to be tagged and treated as equivalent for allocation purposes. For more
information on using the cling policy in conjunction with LVM tags to specify which additional
physical volumes to use when extending an LVM volume, see Section 5.4.14.3, “Extending a
Logical Volume with the cling Allocation Policy”.
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Logical Volume Manager Administration
When a Logical Volume is striped or mirrored, the cling allocation restriction is applied
independently to each stripe or mirror image (leg) that needs space.
An allocation policy of normal will not choose a physical extent that shares the same physical
volume as a logical extent already allocated to a parallel logical volume (that is, a different stripe
or mirror image/leg) at the same offset within that parallel logical volume.
When allocating a mirror log at the same time as logical volumes to hold the mirror data, an
allocation policy of normal will first try to select different physical volumes for the log and the
data. If that is not possible and the allocation/mirror_logs_require_separate_pvs
configuration parameter is set to 0, it will then allow the log to share physical volume(s) with part
of the data.
Similarly, when allocating thin pool metadata, an allocation policy of normal will follow the same
considerations as for allocation of a mirror log, based on the value of the
allocation/thin_pool_metadata_require_separate_pvs configuration parameter.
If there are sufficient free extents to satisfy an allocation request but a normal allocation policy
would not use them, the anywhere allocation policy will, even if that reduces performance by
placing two stripes on the same physical volume.
The allocation policies can be changed using the vgchange command.
NOTE
If you rely upon any layout behavior beyond that documented in this section according to
the defined allocation policies, you should note that this might change in future versions of
the code. For example, if you supply on the command line two empty physical volumes
that have an identical number of free physical extents available for allocation, LVM
currently considers using each of them in the order they are listed; there is no guarantee
that future releases will maintain that property. If it is important to obtain a specific layout
for a particular Logical Volume, then you should build it up through a sequence of
lvcreate and lvconvert steps such that the allocation policies applied to each step
leave LVM no discretion over the layout.
To view the way the allocation process currently works in any specific case, you can read the debug
logging output, for example by adding the -vvvv option to a command.
5.3.3. Creating Volume Groups in a Cluster
You create volume groups in a cluster environment with the vgcreate command, just as you create
them on a single node.
By default, volume groups created with CLVM on shared storage are visible to all computers that have
access to the shared storage. It is possible, however, to create volume groups that are local, visible only
to one node in the cluster, by using the -c n option of the vgcreate command.
The following command, when executed in a cluster environment, creates a volume group that is local to
the node from which the command was executed. The command creates a local volume named vg1 that
contains physical volumes /dev/sdd1 and /dev/sde1.
# vgcreate -c n vg1 /dev/sdd1 /dev/sde1
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You can change whether an existing volume group is local or clustered with the -c option of the
vgchange command, which is described in Section 5.3.8, “Changing the Parameters of a Volume
Group”.
You can check whether an existing volume group is a clustered volume group with the vgs command,
which displays the c attribute if the volume is clustered. The following command displays the attributes of
the volume groups VolGroup00 and testvg1. In this example, VolGroup00 is not clustered, while
testvg1 is clustered, as indicated by the c attribute under the Attr heading.
# vgs
VG
VolGroup00
testvg1
#PV #LV #SN Attr
VSize VFree
1
2
0 wz--n- 19.88G
0
1
1
0 wz--nc 46.00G 8.00M
For more information on the vgs command, see Section 5.3.5, “Displaying Volume Groups”Section 5.8,
“Customized Reporting for LVM”, and the vgs man page.
5.3.4. Adding Physical Volumes to a Volume Group
To add additional physical volumes to an existing volume group, use the vgextend command. The
vgextend command increases a volume group's capacity by adding one or more free physical volumes.
The following command adds the physical volume /dev/sdf1 to the volume group vg1.
# vgextend vg1 /dev/sdf1
5.3.5. Displaying Volume Groups
There are two commands you can use to display properties of LVM volume groups: vgs and
vgdisplay.
The vgscan command, which scans all the disks for volume groups and rebuilds the LVM cache file,
also displays the volume groups. For information on the vgscan command, see Section 5.3.6,
“Scanning Disks for Volume Groups to Build the Cache File”.
The vgs command provides volume group information in a configurable form, displaying one line per
volume group. The vgs command provides a great deal of format control, and is useful for scripting. For
information on using the vgs command to customize your output, see Section 5.8, “Customized
Reporting for LVM”.
The vgdisplay command displays volume group properties (such as size, extents, number of physical
volumes, and so on) in a fixed form. The following example shows the output of a vgdisplay command
for the volume group new_vg. If you do not specify a volume group, all existing volume groups are
displayed.
# vgdisplay new_vg
--- Volume group --VG Name
System ID
Format
Metadata Areas
Metadata Sequence No
VG Access
new_vg
lvm2
3
11
read/write
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VG Status
MAX LV
Cur LV
Open LV
Max PV
Cur PV
Act PV
VG Size
PE Size
Total PE
Alloc PE / Size
Free PE / Size
VG UUID
resizable
0
1
0
0
3
3
51.42 GB
4.00 MB
13164
13 / 52.00 MB
13151 / 51.37 GB
jxQJ0a-ZKk0-OpMO-0118-nlwO-wwqd-fD5D32
5.3.6. Scanning Disks for Volume Groups to Build the Cache File
The vgscan command scans all supported disk devices in the system looking for LVM physical volumes
and volume groups. This builds the LVM cache file in the /etc/lvm/cache/.cache file, which
maintains a listing of current LVM devices.
LVM runs the vgscan command automatically at system startup and at other times during LVM
operation, such as when you execute a vgcreate command or when LVM detects an inconsistency.
NOTE
You may need to run the vgscan command manually when you change your hardware
configuration and add or delete a device from a node, causing new devices to be visible to
the system that were not present at system bootup. This may be necessary, for example,
when you add new disks to the system on a SAN or hotplug a new disk that has been
labeled as a physical volume.
You can define a filter in the lvm.conf file to restrict the scan to avoid specific devices. For information
on using filters to control which devices are scanned, see Section 5.5, “Controlling LVM Device Scans
with Filters”.
The following example shows the output of a vgscan command.
# vgscan
Reading all physical volumes. This may take a while...
Found volume group "new_vg" using metadata type lvm2
Found volume group "officevg" using metadata type lvm2
5.3.7. Removing Physical Volumes from a Volume Group
To remove unused physical volumes from a volume group, use the vgreduce command. The
vgreduce command shrinks a volume group's capacity by removing one or more empty physical
volumes. This frees those physical volumes to be used in different volume groups or to be removed from
the system.
Before removing a physical volume from a volume group, you can make sure that the physical volume is
not used by any logical volumes by using the pvdisplay command.
# pvdisplay /dev/hda1
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-- Physical volume --PV Name
/dev/hda1
VG Name
myvg
PV Size
1.95 GB / NOT usable 4 MB [LVM: 122 KB]
PV#
1
PV Status
available
Allocatable
yes (but full)
Cur LV
1
PE Size (KByte)
4096
Total PE
499
Free PE
0
Allocated PE
499
PV UUID
Sd44tK-9IRw-SrMC-MOkn-76iP-iftz-OVSen7
If the physical volume is still being used you will have to migrate the data to another physical volume
using the pvmove command. Then use the vgreduce command to remove the physical volume.
The following command removes the physical volume /dev/hda1 from the volume group
my_volume_group.
# vgreduce my_volume_group /dev/hda1
If a logical volume contains a physical volume that fails, you cannot use that logical volume. To remove
missing physical volumes from a volume group, you can use the --removemissing parameter of the
vgreduce command, if there are no logical volumes that are allocated on the missing physical volumes.
5.3.8. Changing the Parameters of a Volume Group
The vgchange command is used to deactivate and activate volume groups, as described in
Section 5.3.9, “Activating and Deactivating Volume Groups”. You can also use this command to change
several volume group parameters for an existing volume group.
The following command changes the maximum number of logical volumes of volume group vg00 to 128.
# vgchange -l 128 /dev/vg00
For a description of the volume group parameters you can change with the vgchange command, see
the vgchange(8) man page.
5.3.9. Activating and Deactivating Volume Groups
When you create a volume group it is, by default, activated. This means that the logical volumes in that
group are accessible and subject to change.
There are various circumstances for which you need to make a volume group inactive and thus unknown
to the kernel. To deactivate or activate a volume group, use the -a (--available) argument of the
vgchange command.
The following example deactivates the volume group my_volume_group.
# vgchange -a n my_volume_group
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If clustered locking is enabled, add ’e’ to activate or deactivate a volume group exclusively on one node
or ’l’ to activate or/deactivate a volume group only on the local node. Logical volumes with single-host
snapshots are always activated exclusively because they can only be used on one node at once.
You can deactivate individual logical volumes with the lvchange command, as described in
Section 5.4.10, “Changing the Parameters of a Logical Volume Group”, For information on activating
logical volumes on individual nodes in a cluster, see Section 5.7, “Activating Logical Volumes on
Individual Nodes in a Cluster”.
5.3.10. Removing Volume Groups
To remove a volume group that contains no logical volumes, use the vgremove command.
# vgremove officevg
Volume group "officevg" successfully removed
5.3.11. Splitting a Volume Group
To split the physical volumes of a volume group and create a new volume group, use the vgsplit
command.
Logical volumes cannot be split between volume groups. Each existing logical volume must be entirely
on the physical volumes forming either the old or the new volume group. If necessary, however, you can
use the pvmove command to force the split.
The following example splits off the new volume group smallvg from the original volume group bigvg.
# vgsplit bigvg smallvg /dev/ram15
Volume group "smallvg" successfully split from "bigvg"
5.3.12. Combining Volume Groups
To combine two volume groups into a single volume group, use the vgmerge command. You can merge
an inactive "source" volume with an active or an inactive "destination" volume if the physical extent sizes
of the volume are equal and the physical and logical volume summaries of both volume groups fit into the
destination volume groups limits.
The following command merges the inactive volume group my_vg into the active or inactive volume
group databases giving verbose runtime information.
# vgmerge -v databases my_vg
5.3.13. Backing Up Volume Group Metadata
Metadata backups and archives are automatically created on every volume group and logical volume
configuration change unless disabled in the lvm.conf file. By default, the metadata backup is stored in
the /etc/lvm/backup file and the metadata archives are stored in the /etc/lvm/archives file. You
can manually back up the metadata to the /etc/lvm/backup file with the vgcfgbackup command.
The vgcfrestore command restores the metadata of a volume group from the archive to all the
physical volumes in the volume groups.
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For an example of using the vgcfgrestore command to recover physical volume metadata, see
Section 7.4, “Recovering Physical Volume Metadata”.
5.3.14. Renaming a Volume Group
Use the vgrename command to rename an existing volume group.
Either of the following commands renames the existing volume group vg02 to my_volume_group
# vgrename /dev/vg02 /dev/my_volume_group
# vgrename vg02 my_volume_group
5.3.15. Moving a Volume Group to Another System
You can move an entire LVM volume group to another system. It is recommended that you use the
vgexport and vgimport commands when you do this.
NOTE
As of Red Hat Enterprise Linux 6.5, you can use the --force argument of the vgimport
command. This allows you to import volume groups that are missing physical volumes
and subsequently run the vgreduce --removemissing command.
The vgexport command makes an inactive volume group inaccessible to the system, which allows you
to detach its physical volumes. The vgimport command makes a volume group accessible to a
machine again after the vgexport command has made it inactive.
To move a volume group form one system to another, perform the following steps:
1. Make sure that no users are accessing files on the active volumes in the volume group, then
unmount the logical volumes.
2. Use the -a n argument of the vgchange command to mark the volume group as inactive, which
prevents any further activity on the volume group.
3. Use the vgexport command to export the volume group. This prevents it from being accessed
by the system from which you are removing it.
After you export the volume group, the physical volume will show up as being in an exported
volume group when you execute the pvscan command, as in the following example.
# pvscan
PV /dev/sda1
PV /dev/sdc1
PV /dev/sdd1
...
is in exported VG myvg [17.15 GB / 7.15 GB free]
is in exported VG myvg [17.15 GB / 15.15 GB free]
is in exported VG myvg [17.15 GB / 15.15 GB free]
When the system is next shut down, you can unplug the disks that constitute the volume group
and connect them to the new system.
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4. When the disks are plugged into the new system, use the vgimport command to import the
volume group, making it accessible to the new system.
5. Activate the volume group with the -a y argument of the vgchange command.
6. Mount the file system to make it available for use.
5.3.16. Recreating a Volume Group Directory
To recreate a volume group directory and logical volume special files, use the vgmknodes command.
This command checks the LVM2 special files in the /dev directory that are needed for active logical
volumes. It creates any special files that are missing removes unused ones.
You can incorporate the vgmknodes command into the vgscan command by specifying the mknodes
argument to the vgscan command.
5.4. LOGICAL VOLUME ADMINISTRATION
This section describes the commands that perform the various aspects of logical volume administration.
5.4.1. Creating Linear Logical Volumes
To create a logical volume, use the lvcreate command. If you do not specify a name for the logical
volume, the default name lvol# is used where # is the internal number of the logical volume.
When you create a logical volume, the logical volume is carved from a volume group using the free
extents on the physical volumes that make up the volume group. Normally logical volumes use up any
space available on the underlying physical volumes on a next-free basis. Modifying the logical volume
frees and reallocates space in the physical volumes.
As of the Red Hat Enterprise Linux 6.3 release, you can use LVM to create, display, rename, use, and
remove RAID logical volumes. For information on RAID logical volumes, see Section 5.4.16, “RAID
Logical Volumes”.
The following command creates a logical volume 10 gigabytes in size in the volume group vg1.
# lvcreate -L 10G vg1
The default unit for logical volume size is megabytes. The following command creates a 1500 MB linear
logical volume named testlv in the volume group testvg, creating the block device
/dev/testvg/testlv.
# lvcreate -L 1500 -n testlv testvg
The following command creates a 50 gigabyte logical volume named gfslv from the free extents in
volume group vg0.
# lvcreate -L 50G -n gfslv vg0
You can use the -l argument of the lvcreate command to specify the size of the logical volume in
extents. You can also use this argument to specify the percentage of the volume group to use for the
logical volume. The following command creates a logical volume called mylv that uses 60% of the total
space in volume group testvg.
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# lvcreate -l 60%VG -n mylv testvg
You can also use the -l argument of the lvcreate command to specify the percentage of the
remaining free space in a volume group as the size of the logical volume. The following command
creates a logical volume called yourlv that uses all of the unallocated space in the volume group
testvg.
# lvcreate -l 100%FREE -n yourlv testvg
You can use -l argument of the lvcreate command to create a logical volume that uses the entire
volume group. Another way to create a logical volume that uses the entire volume group is to use the
vgdisplay command to find the "Total PE" size and to use those results as input to the lvcreate
command.
The following commands create a logical volume called mylv that fills the volume group named testvg.
# vgdisplay testvg | grep "Total PE"
Total PE
10230
# lvcreate -l 10230 testvg -n mylv
The underlying physical volumes used to create a logical volume can be important if the physical volume
needs to be removed, so you may need to consider this possibility when you create the logical volume.
For information on removing a physical volume from a volume group, see Section 5.3.7, “Removing
Physical Volumes from a Volume Group”.
To create a logical volume to be allocated from a specific physical volume in the volume group, specify
the physical volume or volumes at the end at the lvcreate command line. The following command
creates a logical volume named testlv in volume group testvg allocated from the physical volume
/dev/sdg1,
# lvcreate -L 1500 -ntestlv testvg /dev/sdg1
You can specify which extents of a physical volume are to be used for a logical volume. The following
example creates a linear logical volume out of extents 0 through 24 of physical volume /dev/sda1 and
extents 50 through 124 of physical volume /dev/sdb1 in volume group testvg.
# lvcreate -l 100 -n testlv testvg /dev/sda1:0-24 /dev/sdb1:50-124
The following example creates a linear logical volume out of extents 0 through 25 of physical volume
/dev/sda1 and then continues laying out the logical volume at extent 100.
# lvcreate -l 100 -n testlv testvg /dev/sda1:0-25:100The default policy for how the extents of a logical volume are allocated is inherit, which applies the
same policy as for the volume group. These policies can be changed using the lvchange command.
For information on allocation policies, see Section 5.3.1, “Creating Volume Groups”.
5.4.2. Creating Striped Volumes
For large sequential reads and writes, creating a striped logical volume can improve the efficiency of the
data I/O. For general information about striped volumes, see Section 3.3.2, “Striped Logical Volumes”.
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When you create a striped logical volume, you specify the number of stripes with the -i argument of the
lvcreate command. This determines over how many physical volumes the logical volume will be
striped. The number of stripes cannot be greater than the number of physical volumes in the volume
group (unless the --alloc anywhere argument is used).
If the underlying physical devices that make up a striped logical volume are different sizes, the maximum
size of the striped volume is determined by the smallest underlying device. For example, in a two-legged
stripe, the maximum size is twice the size of the smaller device. In a three-legged stripe, the maximum
size is three times the size of the smallest device.
The following command creates a striped logical volume across 2 physical volumes with a stripe of 64kB.
The logical volume is 50 gigabytes in size, is named gfslv, and is carved out of volume group vg0.
# lvcreate -L 50G -i2 -I64 -n gfslv vg0
As with linear volumes, you can specify the extents of the physical volume that you are using for the
stripe. The following command creates a striped volume 100 extents in size that stripes across two
physical volumes, is named stripelv and is in volume group testvg. The stripe will use sectors 0-49
of /dev/sda1 and sectors 50-99 of /dev/sdb1.
# lvcreate -l 100 -i2 -nstripelv testvg /dev/sda1:0-49 /dev/sdb1:50-99
Using default stripesize 64.00 KB
Logical volume "stripelv" created
5.4.3. Creating Mirrored Volumes
NOTE
As of the Red Hat Enterprise Linux 6.3 release, LVM supports RAID4/5/6 and a new
implementation of mirroring. For information on this new implementation, see
Section 5.4.16, “RAID Logical Volumes”.
NOTE
Creating a mirrored LVM logical volume in a cluster requires the same commands and
procedures as creating a mirrored LVM logical volume on a single node. However, in
order to create a mirrored LVM volume in a cluster the cluster and cluster mirror
infrastructure must be running, the cluster must be quorate, and the locking type in the
lvm.conf file must be set correctly to enable cluster locking. For an example of creating
a mirrored volume in a cluster, see Section 6.5, “Creating a Mirrored LVM Logical Volume
in a Cluster”.
Attempting to run multiple LVM mirror creation and conversion commands in quick
succession from multiple nodes in a cluster might cause a backlog of these commands.
This might cause some of the requested operations to time-out and, subsequently, fail. To
avoid this issue, it is recommended that cluster mirror creation commands be executed
from one node of the cluster.
When you create a mirrored volume, you specify the number of copies of the data to make with the -m
argument of the lvcreate command. Specifying -m1 creates one mirror, which yields two copies of the
file system: a linear logical volume plus one copy. Similarly, specifying -m2 creates two mirrors, yielding
three copies of the file system.
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The following command creates a mirrored logical volume with a single mirror. The volume is 50
gigabytes in size, is named mirrorlv, and is carved out of volume group vg0:
# lvcreate -L 50G -m1 -n mirrorlv vg0
An LVM mirror divides the device being copied into regions that, by default, are 512KB in size. You can
use the -R argument of the lvcreate command to specify the region size in megabytes. You can also
change the default region size by editing the mirror_region_size setting in the lvm.conf file.
NOTE
Due to limitations in the cluster infrastructure, cluster mirrors greater than 1.5TB cannot be
created with the default region size of 512KB. Users that require larger mirrors should
increase the region size from its default to something larger. Failure to increase the
region size will cause LVM creation to hang and may hang other LVM commands as well.
As a general guideline for specifying the region size for mirrors that are larger than 1.5TB,
you could take your mirror size in terabytes and round up that number to the next power of
2, using that number as the -R argument to the lvcreate command. For example, if
your mirror size is 1.5TB, you could specify -R 2. If your mirror size is 3TB, you could
specify -R 4. For a mirror size of 5TB, you could specify -R 8.
The following command creates a mirrored logical volume with a region size of 2MB:
# lvcreate -m1 -L 2T -R 2 -n mirror vol_group
When a mirror is created, the mirror regions are synchronized. For large mirror components, the sync
process may take a long time. As of the Red Hat Enterprise Linux 6.3 release, When you are creating a
new mirror that does not need to be revived, you can specify the --nosync argument to indicate that an
initial synchronization from the first device is not required.
LVM maintains a small log which it uses to keep track of which regions are in sync with the mirror or
mirrors. By default, this log is kept on disk, which keeps it persistent across reboots and ensures that the
mirror does not need to be resynced every time a machine reboots or crashes. You can specify instead
that this log be kept in memory with the --mirrorlog core argument; this eliminates the need for an
extra log device, but it requires that the entire mirror be resynchronized at every reboot.
The following command creates a mirrored logical volume from the volume group bigvg. The logical
volume is named ondiskmirvol and has a single mirror. The volume is 12MB in size and keeps the
mirror log in memory.
# lvcreate -L 12MB -m1 --mirrorlog core -n ondiskmirvol bigvg
Logical volume "ondiskmirvol" created
The mirror log is created on a separate device from the devices on which any of the mirror legs are
created. It is possible, however, to create the mirror log on the same device as one of the mirror legs by
using the --alloc anywhere argument of the vgcreate command. This may degrade performance,
but it allows you to create a mirror even if you have only two underlying devices.
The following command creates a mirrored logical volume with a single mirror for which the mirror log is
on the same device as one of the mirror legs. In this example, the volume group vg0 consists of only two
devices. This command creates a 500 MB volume named mirrorlv in the vg0 volume group.
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Logical Volume Manager Administration
# lvcreate -L 500M -m1 -n mirrorlv -alloc anywhere vg0
NOTE
With clustered mirrors, the mirror log management is completely the responsibility of the
cluster node with the currently lowest cluster ID. Therefore, when the device holding the
cluster mirror log becomes unavailable on a subset of the cluster, the clustered mirror can
continue operating without any impact, as long as the cluster node with lowest ID retains
access to the mirror log. Since the mirror is undisturbed, no automatic corrective action
(repair) is issued, either. When the lowest-ID cluster node loses access to the mirror log,
however, automatic action will kick in (regardless of accessibility of the log from other
nodes).
To create a mirror log that is itself mirrored, you can specify the --mirrorlog mirrored argument.
The following command creates a mirrored logical volume from the volume group bigvg. The logical
volume is named twologvol and has a single mirror. The volume is 12MB in size and the mirror log is
mirrored, with each log kept on a separate device.
# lvcreate -L 12MB -m1 --mirrorlog mirrored -n twologvol bigvg
Logical volume "twologvol" created
Just as with a standard mirror log, it is possible to create the redundant mirror logs on the same device
as the mirror legs by using the --alloc anywhere argument of the vgcreate command. This may
degrade performance, but it allows you to create a redundant mirror log even if you do not have
sufficient underlying devices for each log to be kept on a separate device than the mirror legs.
When a mirror is created, the mirror regions are synchronized. For large mirror components, the sync
process may take a long time. When you are creating a new mirror that does not need to be revived, you
can specify the --nosync argument to indicate that an initial synchronization from the first device is not
required.
You can specify which devices to use for the mirror legs and log, and which extents of the devices to use.
To force the log onto a particular disk, specify exactly one extent on the disk on which it will be placed.
LVM does not necessary respect the order in which devices are listed in the command line. If any
physical volumes are listed that is the only space on which allocation will take place. Any physical extents
included in the list that are already allocated will get ignored.
The following command creates a mirrored logical volume with a single mirror and a single log that is not
mirrored. The volume is 500 MB in size, it is named mirrorlv, and it is carved out of volume group
vg0. The first leg of the mirror is on device /dev/sda1, the second leg of the mirror is on device
/dev/sdb1, and the mirror log is on /dev/sdc1.
# lvcreate -L 500M -m1 -n mirrorlv vg0 /dev/sda1 /dev/sdb1 /dev/sdc1
The following command creates a mirrored logical volume with a single mirror. The volume is 500 MB in
size, it is named mirrorlv, and it is carved out of volume group vg0. The first leg of the mirror is on
extents 0 through 499 of device /dev/sda1, the second leg of the mirror is on extents 0 through 499 of
device /dev/sdb1, and the mirror log starts on extent 0 of device /dev/sdc1. These are 1MB extents.
If any of the specified extents have already been allocated, they will be ignored.
# lvcreate -L 500M -m1 -n mirrorlv vg0 /dev/sda1:0-499 /dev/sdb1:0-499
/dev/sdc1:0
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
NOTE
As of the Red Hat Enterprise Linux 6.1 release, you can combine striping and mirroring in
a single logical volume. Creating a logical volume while simultaneously specifying the
number of mirrors (--mirrors X) and the number of stripes (--stripes Y) results in a
mirror device whose constituent devices are striped.
5.4.3.1. Mirrored Logical Volume Failure Policy
You can define how a mirrored logical volume behaves in the event of a device failure with the
mirror_image_fault_policy and mirror_log_fault_policy parameters in the activation
section of the lvm.conf file. When these parameters are set to remove, the system attempts to
remove the faulty device and run without it. When this parameter is set to allocate, the system
attempts to remove the faulty device and tries to allocate space on a new device to be a replacement for
the failed device; this policy acts like the remove policy if no suitable device and space can be allocated
for the replacement.
By default, the mirror_log_fault_policy parameter is set to allocate. Using this policy for the
log is fast and maintains the ability to remember the sync state through crashes and reboots. If you set
this policy to remove, when a log device fails the mirror converts to using an in-memory log and the
mirror will not remember its sync status across crashes and reboots and the entire mirror will be
resynced.
By default, the mirror_image_fault_policy parameter is set to remove. With this policy, if a mirror
image fails the mirror will convert to a non-mirrored device if there is only one remaining good copy.
Setting this policy to allocate for a mirror device requires the mirror to resynchronize the devices; this
is a slow process, but it preserves the mirror characteristic of the device.
NOTE
When an LVM mirror suffers a device failure, a two-stage recovery takes place. The first
stage involves removing the failed devices. This can result in the mirror being reduced to
a linear device. The second stage, if the mirror_log_fault_policy parameter is set
to allocate, is to attempt to replace any of the failed devices. Note, however, that there
is no guarantee that the second stage will choose devices previously in-use by the mirror
that had not been part of the failure if others are available.
For information on manually recovering from an LVM mirror failure, see Section 7.3,
“Recovering from LVM Mirror Failure”.
5.4.3.2. Splitting Off a Redundant Image of a Mirrored Logical Volume
You can split off a redundant image of a mirrored logical volume to form a new logical volume. To split
off an image, you use the --splitmirrors argument of the lvconvert command, specifying the
number of redundant images to split off. You must use the --name argument of the command to specify
a name for the newly-split-off logical volume.
The following command splits off a new logical volume named copy from the mirrored logical volume
vg/lv. The new logical volume contains two mirror legs. In this example, LVM selects which devices to
split off.
# lvconvert --splitmirrors 2 --name copy vg/lv
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You can specify which devices to split off. The following command splits off a new logical volume named
copy from the mirrored logical volume vg/lv. The new logical volume contains two mirror legs
consisting of devices /dev/sdc1 and /dev/sde1.
# lvconvert --splitmirrors 2 --name copy vg/lv /dev/sd[ce]1
5.4.3.3. Repairing a Mirrored Logical Device
You can use the lvconvert --repair command to repair a mirror after a disk failure. This brings the
mirror back into a consistent state. The lvconvert --repair command is an interactive command
that prompts you to indicate whether you want the system to attempt to replace any failed devices.
To skip the prompts and replace all of the failed devices, specify the -y option on the command
line.
To skip the prompts and replace none of the failed devices, specify the -f option on the
command line.
To skip the prompts and still indicate different replacement policies for the mirror image and the
mirror log, you can specify the --use-policies argument to use the device replacement
policies specified by the mirror_log_fault_policy and mirror_device_fault_policy
parameters in the lvm.conf file.
5.4.3.4. Changing Mirrored Volume Configuration
You can increase or decrease the number of mirrors that a logical volume contains by using the
lvconvert command. This allows you to convert a logical volume from a mirrored volume to a linear
volume or from a linear volume to a mirrored volume. You can also use this command to reconfigure
other mirror parameters of an existing logical volume, such as corelog.
When you convert a linear volume to a mirrored volume, you are creating mirror legs for an existing
volume. This means that your volume group must contain the devices and space for the mirror legs and
for the mirror log.
If you lose a leg of a mirror, LVM converts the volume to a linear volume so that you still have access to
the volume, without the mirror redundancy. After you replace the leg, you can use the lvconvert
command to restore the mirror. This procedure is provided in Section 7.3, “Recovering from LVM Mirror
Failure”.
The following command converts the linear logical volume vg00/lvol1 to a mirrored logical volume.
# lvconvert -m1 vg00/lvol1
The following command converts the mirrored logical volume vg00/lvol1 to a linear logical volume,
removing the mirror leg.
# lvconvert -m0 vg00/lvol1
The following example adds an additional mirror leg to the existing logical volume vg00/lvol1. This
example shows the configuration of the volume before and after the lvconvert command changed the
volume to a volume with two mirror legs.
# lvs -a -o name,copy_percent,devices vg00
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
LV
Copy% Devices
lvol1
100.00 lvol1_mimage_0(0),lvol1_mimage_1(0)
[lvol1_mimage_0]
/dev/sda1(0)
[lvol1_mimage_1]
/dev/sdb1(0)
[lvol1_mlog]
/dev/sdd1(0)
# lvconvert -m 2 vg00/lvol1
vg00/lvol1: Converted: 13.0%
vg00/lvol1: Converted: 100.0%
Logical volume lvol1 converted.
# lvs -a -o name,copy_percent,devices vg00
LV
Copy% Devices
lvol1
100.00
lvol1_mimage_0(0),lvol1_mimage_1(0),lvol1_mimage_2(0)
[lvol1_mimage_0]
/dev/sda1(0)
[lvol1_mimage_1]
/dev/sdb1(0)
[lvol1_mimage_2]
/dev/sdc1(0)
[lvol1_mlog]
/dev/sdd1(0)
5.4.4. Creating Thinly-Provisioned Logical Volumes
As of the Red Hat Enterprise Linux 6.4 release, logical volumes can be thinly provisioned. This allows
you to create logical volumes that are larger than the available extents. Using thin provisioning, you can
manage a storage pool of free space, known as a thin pool, which can be allocated to an arbitrary
number of devices when needed by applications. You can then create devices that can be bound to the
thin pool for later allocation when an application actually writes to the logical volume. The thin pool can
be expanded dynamically when needed for cost-effective allocation of storage space.
NOTE
This section provides an overview of the basic commands you use to create and grow
thinly-provisioned logical volumes. For detailed information on LVM thin provisioning as
well as information on using the LVM commands and utilities with thinly-provisioned
logical volumes, see the lvmthin(7) man page.
NOTE
Thin volumes are not supported across the nodes in a cluster. The thin pool and all its thin
volumes must be exclusively activated on only one cluster node.
To create a thin volume, you perform the following tasks:
1. Create a volume group with the vgcreate command.
2. Create a thin pool with the lvcreate command.
3. Create a thin volume in the thin pool with the lvcreate command.
You can use the -T (or --thin) option of the lvcreate command to create either a thin pool or a thin
volume. You can also use -T option of the lvcreate command to create both a thin pool and a thin
volume in that pool at the same time with a single command.
The following command uses the -T option of the lvcreate command to create a thin pool named
mythinpool that is in the volume group vg001 and that is 100M in size. Note that since you are
creating a pool of physical space, you must specify the size of the pool. The -T option of the lvcreate
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Logical Volume Manager Administration
command does not take an argument; it deduces what type of device is to be created from the other
options the command specifies.
# lvcreate -L 100M -T vg001/mythinpool
Rounding up size to full physical extent 4.00 MiB
Logical volume "mythinpool" created
# lvs
LV
VG
Attr
LSize
Pool Origin Data% Move Log Copy%
Convert
my mythinpool vg001 twi-a-tz 100.00m
0.00
The following command uses the -T option of the lvcreate command to create a thin volume named
thinvolume in the thin pool vg001/mythinpool. Note that in this case you are specifying virtual size,
and that you are specifying a virtual size for the volume that is greater than the pool that contains it.
# lvcreate -V1G -T vg001/mythinpool -n thinvolume
Logical volume "thinvolume" created
# lvs
LV
VG
Attr
LSize
Pool
Origin Data% Move
Log Copy% Convert
mythinpool vg001
twi-a-tz 100.00m
0.00
thinvolume vg001
Vwi-a-tz
1.00g mythinpool
0.00
The following command uses the -T option of the lvcreate command to create a thin pool and a thin
volume in that pool by specifying both a size and a virtual size argument for the lvcreate command.
This command creates a thin pool named mythinpool in the volume group vg001 and it also creates a
thin volume named thinvolume in that pool.
# lvcreate -L 100M -T vg001/mythinpool -V1G -n thinvolume
Rounding up size to full physical extent 4.00 MiB
Logical volume "thinvolume" created
# lvs
LV
VG
Attr
LSize
Pool
Origin Data% Move Log
Copy% Convert
mythinpool
vg001
twi-a-tz 100.00m
0.00
thinvolume
vg001
Vwi-a-tz
1.00g mythinpool
0.00
You can also create a thin pool by specifying the --thinpool parameter of the lvcreate command.
Unlike the -T option, the --thinpool parameter requires an argument, which is the name of the thin
pool logical volume that you are creating. The following example specifies the --thinpool parameter
of the lvcreate command to create a thin pool named mythinpool that is in the volume group vg001
and that is 100M in size:
# lvcreate -L 100M --thinpool mythinpool vg001
Rounding up size to full physical extent 4.00 MiB
Logical volume "mythinpool" created
# lvs
LV
VG
Attr
LSize
Pool Origin Data% Move Log Copy%
Convert
mythinpool vg001 twi-a-tz 100.00m
0.00
Striping is supported for pool creation. The following command creates a 100M thin pool named pool in
volume group vg001 with two 64 kB stripes and a chunk size of 256 kB. It also creates a 1T thin volume,
vg00/thin_lv.
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
# lvcreate -i 2 -I 64 -c 256 -L100M -T vg00/pool -V 1T --name thin_lv
You can extend the size of a thin volume with the lvextend command. You cannot, however, reduce
the size of a thin pool.
The following command resizes an existing thin pool that is 100M in size by extending it another 100M.
# lvextend -L+100M vg001/mythinpool
Extending logical volume mythinpool to
Logical volume mythinpool successfully
# lvs
LV
VG
Attr
LSize
Copy% Convert
mythinpool
vg001
twi-a-tz 200.00m
thinvolume
vg001
Vwi-a-tz
1.00g
200.00 MiB
resized
Pool
Origin Data%
mythinpool
Move Log
0.00
0.00
As with other types of logical volumes, you can rename the volume with the lvrename, you can remove
the volume with the lvremove, and you can display information about the volume with the lvs and
lvdisplay commands.
By default, the lvcreate command sets the size of the thin pool's metadata logical volume according to
the formula (Pool_LV_size / Pool_LV_chunk_size * 64). You cannot currently resize the metadata
volume, however, so if you expect significant growth of the size of thin pool at a later time you should
increase this value with the --poolmetadatasize parameter of the lvcreate command. The
supported value for the thin pool's metadata logical volume is in the range between 2MiB and 16GiB.
You can use the --thinpool parameter of the lvconvert command to convert an existing logical
volume to a thin pool volume. When you convert an existing logical volume to a thin pool volume, you
must use the --poolmetadata parameter in conjunction with the --thinpool parameter of the
lvconvert to convert an existing logical volume to the thin pool volume's metadata volume.
NOTE
Converting a logical volume to a thin pool volume or a thin pool metadata volume destroys
the content of the logical volume, since in this case the lvconvert does not preserve the
content of the devices but instead overwrites the content.
The following example converts the existing logical volume lv1 in volume group vg001 to a thin pool
volume and converts the existing logical volume lv2 in volume group vg001 to the metadata volume for
that thin pool volume.
# lvconvert --thinpool vg001/lv1 --poolmetadata vg001/lv2
Converted vg001/lv1 to thin pool.
5.4.5. Creating Snapshot Volumes
NOTE
As of the Red Hat Enterprise Linux 6.4 release, LVM supports thinly-provisioned
snapshots. For information on creating thinly provisioned snapshot volumes, see
Section 5.4.6, “Creating Thinly-Provisioned Snapshot Volumes”.
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Logical Volume Manager Administration
Use the -s argument of the lvcreate command to create a snapshot volume. A snapshot volume is
writable.
NOTE
LVM snapshots are not supported across the nodes in a cluster. You cannot create a
snapshot volume in a clustered volume group. As of the Red Hat Enterprise Linux 6.1
release, however, if you need to create a consistent backup of data on a clustered logical
volume you can activate the volume exclusively and then create the snapshot. For
information on activating logical volumes exclusively on one node, see Section 5.7,
“Activating Logical Volumes on Individual Nodes in a Cluster”.
NOTE
As of the Red Hat Enterprise Linux 6.1 release, LVM snapshots are supported for
mirrored logical volumes.
As of the Red Hat Enterprise Linux 6.3 release, snapshots are supported for RAID logical
volumes. For information on RAID logical volumes, see Section 5.4.16, “RAID Logical
Volumes”.
As of the Red Hat Enterprise Linux 6.5 release, LVM does not allow you to create a snapshot volume
that is larger than the size of the origin volume plus needed metadata for the volume. If you specify a
snapshot volume that is larger than this, the system will create a snapshot volume that is only as large as
will be needed for the size of the origin.
By default, a snapshot volume is skipped during normal activation commands. For information on
controlling the activation of a snapshot volume, see Section 5.4.17, “Controlling Logical Volume
Activation”.
The following command creates a snapshot logical volume that is 100 MB in size named
/dev/vg00/snap. This creates a snapshot of the origin logical volume named /dev/vg00/lvol1. If
the original logical volume contains a file system, you can mount the snapshot logical volume on an
arbitrary directory in order to access the contents of the file system to run a backup while the original file
system continues to get updated.
# lvcreate --size 100M --snapshot --name snap /dev/vg00/lvol1
After you create a snapshot logical volume, specifying the origin volume on the lvdisplay command
yields output that includes a list of all snapshot logical volumes and their status (active or inactive).
The following example shows the status of the logical volume /dev/new_vg/lvol0, for which a
snapshot volume /dev/new_vg/newvgsnap has been created.
# lvdisplay /dev/new_vg/lvol0
--- Logical volume --LV Name
/dev/new_vg/lvol0
VG Name
new_vg
LV UUID
LBy1Tz-sr23-OjsI-LT03-nHLC-y8XW-EhCl78
LV Write Access
read/write
LV snapshot status
source of
/dev/new_vg/newvgsnap1 [active]
LV Status
available
# open
0
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
LV Size
Current LE
Segments
Allocation
Read ahead sectors
Block device
52.00 MB
13
1
inherit
0
253:2
The lvs command, by default, displays the origin volume and the current percentage of the snapshot
volume being used for each snapshot volume. The following example shows the default output for the
lvs command for a system that includes the logical volume /dev/new_vg/lvol0, for which a
snapshot volume /dev/new_vg/newvgsnap has been created.
# lvs
LV
VG
Attr
LSize Origin Snap% Move Log Copy%
lvol0
new_vg owi-a- 52.00M
newvgsnap1 new_vg swi-a- 8.00M lvol0
0.20

WARNING
Because the snapshot increases in size as the origin volume changes, it is
important to monitor the percentage of the snapshot volume regularly with the lvs
command to be sure it does not fill. A snapshot that is 100% full is lost completely,
as a write to unchanged parts of the origin would be unable to succeed without
corrupting the snapshot.
As of the Red Hat Enterprise Linux 6.2 release, there are two new features related to snapshots. First, in
addition to the snapshot itself being invalidated when full, any mounted file systems on that snapshot
device are forcibly unmounted, avoiding the inevitable file system errors upon access to the mount point.
Second, you can specify the snapshot_autoextend_threshold option in the lvm.conf file. This
option allows automatic extension of a snapshot whenever the remaining snapshot space drops below
the threshold you set. This feature requires that there be unallocated space in the volume group.
As of the Red Hat Enterprise Linux 6.5 release, LVM does not allow you to create a snapshot volume
that is larger than the size of the origin volume plus needed metadata for the volume. Similarly,
automatic extension of a snapshot will not increase the size of a snapshot volume beyond the maximum
calculated size that is necessary for the snapshot. Once a snapshot has grown large enough to cover the
origin, it is no longer monitored for automatic extension.
Information on setting snapshot_autoextend_threshold and snapshot_autoextend_percent
is provided in the lvm.conf file itself. For information about the lvm.conf file, see Appendix B, The
LVM Configuration Files.
5.4.6. Creating Thinly-Provisioned Snapshot Volumes
The Red Hat Enterprise Linux release 6.4 version of LVM provides support for thinly-provisioned
snapshot volumes. For information on the benefits and limitations of thin snapshot volumes, see
Section 3.3.7, “Thinly-Provisioned Snapshot Volumes”.
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Logical Volume Manager Administration
NOTE
This section provides an overview of the basic commands you use to create and grow
thinly-provisioned snapshot volumes. For detailed information on LVM thin provisioning
as well as information on using the LVM commands and utilities with thinly-provisioned
logical volumes, see the lvmthin(7) man page.
IMPORTANT
When creating a thin snapshot volume, you do not specify the size of the volume. If you
specify a size parameter, the snapshot that will be created will not be a thin snapshot
volume and will not use the thin pool for storing data. For example, the command
lvcreate -s vg/thinvolume -L10M will not create a thin snapshot, even though the
origin volume is a thin volume.
Thin snapshots can be created for thinly-provisioned origin volumes. As of the Red Hat Enterprise Linux
6.5 release, thin snapshots can also be created for origin volumes that are not thinly-provisioned.
You can specify a name for the snapshot volume with the --name option of the lvcreate command. It
is recommended that you use this option when creating a logical volume so that you can more easily see
the volume you have created when you display logical volumes with the lvs command.
The following command creates a thinly-provisioned snapshot volume of the thinly-provisioned logical
volume vg001/thinvolume that is named mysnapshot1.
# lvcreate -s --name mysnapshot1 vg001/thinvolume
Logical volume "mysnapshot1" created
# lvs
LV
VG
Attr
LSize
Pool
Origin
Data%
Move Log Copy% Convert
mysnapshot1 vg001
Vwi-a-tz
1.00g mythinpool thinvolume
0.00
mythinpool vg001
twi-a-tz 100.00m
0.00
thinvolume vg001
Vwi-a-tz
1.00g mythinpool
0.00
A thin snapshot volume has the same characteristics as any other thin volume. You can independently
activate the volume, extend the volume, rename the volume, remove the volume, and even snapshot the
volume.
By default, a snapshot volume is skipped during normal activation commands. For information on
controlling the activation of a snapshot volume, see Section 5.4.17, “Controlling Logical Volume
Activation”.
As of the Red Hat Enterprise Linux 6.5 release, you can create a thinly-provisioned snapshot of a nonthinly-provisioned logical volume. Since the non-thinly-provisioned logical volume is not contained within
a thinpool, it is referred to as an external origin. External origin volumes can be used and shared by
many thinly-provisioned snapshot volumes, even from different thin pools. The external origin must be
inactive and read-only at the time the thinly-provisioned snapshot is created.
To create a thinly-provisioned snapshot of an external origin, you must specify the --thinpool option.
The following command creates a thin snapshot volume of the read-only inactive volume
origin_volume. The thin snapshot volume is named mythinsnap. The logical volume
origin_volume then becomes the thin external origin for the thin shapshot volume mythinsnap in
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
volume group vg001 that will use the existing thin pool vg001/pool. Because the origin volume must
be in the same volume group as the snapshot volume, you do not need to specify the volume group
when specifying the origin logical volume.
# lvcreate -s --thinpool vg001/pool origin_volume --name mythinsnap
You can create a second thinly-provisioned snapshot volume of the first snapshot volume, as in the
following command.
# lvcreate -s vg001/mythinsnap --name my2ndthinsnap
5.4.7. Creating LVM Cache Logical Volumes
As of the Red Hat Enterprise Linux 6.7 release, LVM provides full support for LVM cache logical
volumes. A cache logical volume uses a small logical volume consisting of fast block devices (such as
SSD drives) to improve the performance of a larger and slower logical volume by storing the frequently
used blocks on the smaller, faster logical volume.
LVM caching uses the following LVM logical volume types. All of these associated logical volumes must
be in the same volume group.
Origin logical volume — the large, slow logical volume
Cache pool logical volume — the small, fast logical volume, which is composed of two devices:
the cache data logical volume, and the cache metadata logical volume
Cache data logical volume — the logical volume containing the data blocks for the cache pool
logical volume
Cache metadata logical volume — the logical volume containing the metadata for the cache pool
logical volume, which holds the accounting information that specifies where data blocks are
stored (for example, on the origin logical volume or the cache data logical volume).
Cache logical volume — the logical volume containing the origin logical volume and the cache
pool logical volume. This is the resultant usable device which encapsulates the various cache
volume components.
The following procedure creates an LVM cache logical volume.
1. Create a volume group that contains a slow physical volume and a fast physical volume. In this
example. /dev/sde1 is a slow device and /dev/sdf1 is a fast device and both devices are
contained in volume group VG.
# pvcreate /dev/sde1
# pvcreate /dev/sdf1
# vgcreate VG /dev/sde1 /dev/sdf1
2. Create the origin volume. This example creates an origin volume named lv that is 4G in size
and that consists of /dev/sde1, the slow physical volume.
# lvcreate -L 4G -n lv VG /dev/sde1
3. Create the cache data logical volume. This logical volume will hold data blocks from the origin
volume. The size of this logical volume is the size of the cache and will be reported as the size of
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Logical Volume Manager Administration
the cache pool logical volume. This example creates the cache data volume named lv_cache.
It is 2G in size and is contained on the fast device /dev/sdf1, which is part of the volume
group VG.
# lvcreate -L 2G -n lv_cache VG /dev/sdf1
4. Create the cache metadata logical volume. This logical volume will hold cache pool metadata.
This logical volume should be about 1000 time smaller than the cache data logical volume, with a
minimum size of 8MiB. This example creates the cache metadata volume named
lv_cache_meta. It is 12M in size and is also contained on the fast device /dev/sdf1, which
is part of the volume group VG.
# lvcreate -L 12M -n lv_cache_meta VG /dev/sdf1
5. Create the cache pool logical volume by combining the cache data and the cache metadata
logical volumes into a logical volume of type cache-pool. You can set the behavior of the
cache pool in this step; in this example the cachemode argument is set to writethrough,
which indicates that a write is considered complete only when it has been stored in both the
cache pool logical volume and on the origin logical volume.
When you execute this command, the cache data logical volume is renamed with _cdata
appended to the original name of the cache data logical volume, and the cache metadata logical
volume is renamed with _cmeta appended to the original name of the cache data logical
volume; both of these volumes become hidden.
# lvconvert --type cache-pool --cachemode writethrough -poolmetadata VG/lv_cache_meta VG/lv_cache
WARNING: Converting logical volume VG/lv_cache and
VG/lv_cache_meta to pool's data and metadata volumes.
THIS WILL DESTROY CONTENT OF LOGICAL VOLUME (filesystem etc.)
Converted VG/lv_cache to cache pool.
# lvs -a -o +devices
LV
VG Attr
LSize
Pool Origin Data% Meta%
Cpy%Sync Devices
lv
VG -wi-a----4.00g
/dev/sde1(0)
lv_cache
VG Cwi---C--2.00g
lv_cache_cdata(0)
[lv_cache_cdata] VG Cwi------2.00g
/dev/sdf1(0)
[lv_cache_cmeta] VG ewi------- 12.00m
/dev/sdf1(512)
[lvol0_pmspare] VG ewi------- 12.00m
/dev/sde1(1024)
6. Create the cache logical volume by combining the cache pool logical volume with the origin
logical volume. The user-accessible cache logical volume takes the name of the origin logical
volume. The origin logical volume becomes a hidden logical volume with _corig appended to
the original name. You can execute this command when the origin logical volume is in use.
# lvconvert --type cache --cachepool VG/lv_cache VG/lv
Logical volume VG/lv is now cached.
# lvs -a -o +devices
LV
VG Attr
LSize
Pool
Origin
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
Data% Meta% Cpy%Sync Devices
lv
VG Cwi-a-C--4.00g [lv_cache] [lv_corig]
0.02
2.31 0.00
lv_corig(0)
[lv_corig]
VG owi-aoC--4.00g
/dev/sde1(0)
[lv_cache]
VG Cwi---C--2.00g
0.02
2.31 0.00
lv_cache_cdata(0)
[lv_cache_cdata] VG Cwi-ao---2.00g
/dev/sdf1(0)
[lv_cache_cmeta] VG ewi-ao---- 12.00m
/dev/sdf1(512)
[lvol0_pmspare]
VG ewi------- 12.00m
/dev/sde1(1024)
For further information on LVM cache volumes, including additional administrative examples, see the
lvmcache(7) man page.
5.4.8. Merging Snapshot Volumes
As of the Red Hat Enterprise Linux 6 release, you can use the --merge option of the lvconvert
command to merge a snapshot into its origin volume. If both the origin and snapshot volume are not
open, the merge will start immediately. Otherwise, the merge will start the first time either the origin or
snapshot are activated and both are closed. Merging a snapshot into an origin that cannot be closed, for
example a root file system, is deferred until the next time the origin volume is activated. When merging
starts, the resulting logical volume will have the origin’s name, minor number and UUID. While the merge
is in progress, reads or writes to the origin appear as they were directed to the snapshot being merged.
When the merge finishes, the merged snapshot is removed.
The following command merges snapshot volume vg00/lvol1_snap into its origin.
# lvconvert --merge vg00/lvol1_snap
You can specify multiple snapshots on the command line, or you can use LVM object tags to specify that
multiple snapshots be merged to their respective origins. In the following example, logical volumes
vg00/lvol1, vg00/lvol2, and vg00/lvol3 are all tagged with the tag @some_tag. The following
command merges the snapshot logical volumes for all three volumes serially: vg00/lvol1, then
vg00/lvol2, then vg00/lvol3. If the --background option were used, all snapshot logical volume
merges would start in parallel.
# lvconvert --merge @some_tag
For information on tagging LVM objects, see Appendix D, LVM Object Tags. For further information on
the lvconvert --merge command, see the lvconvert(8) man page.
5.4.9. Persistent Device Numbers
Major and minor device numbers are allocated dynamically at module load. Some applications work best
if the block device always is activated with the same device (major and minor) number. You can specify
these with the lvcreate and the lvchange commands by using the following arguments:
--persistent y --major major --minor minor
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Logical Volume Manager Administration
Use a large minor number to be sure that it has not already been allocated to another device
dynamically.
If you are exporting a file system using NFS, specifying the fsid parameter in the exports file may avoid
the need to set a persistent device number within LVM.
5.4.10. Changing the Parameters of a Logical Volume Group
To change the parameters of a logical volume, use the lvchange command. For a listing of the
parameters you can change, see the lvchange(8) man page.
You can use the lvchange command to activate and deactivate logical volumes. To activate and
deactivate all the logical volumes in a volume group at the same time, use the vgchange command, as
described in Section 5.3.8, “Changing the Parameters of a Volume Group”.
The following command changes the permission on volume lvol1 in volume group vg00 to be readonly.
# lvchange -pr vg00/lvol1
5.4.11. Renaming Logical Volumes
To rename an existing logical volume, use the lvrename command.
Either of the following commands renames logical volume lvold in volume group vg02 to lvnew.
# lvrename /dev/vg02/lvold /dev/vg02/lvnew
# lvrename vg02 lvold lvnew
For more information on activating logical volumes on individual nodes in a cluster, see Section 5.7,
“Activating Logical Volumes on Individual Nodes in a Cluster”.
5.4.12. Removing Logical Volumes
To remove an inactive logical volume, use the lvremove command. If the logical volume is currently
mounted, unmount the volume before removing it. In addition, in a clustered environment you must
deactivate a logical volume before it can be removed.
The following command removes the logical volume /dev/testvg/testlv from the volume group
testvg. Note that in this case the logical volume has not been deactivated.
# lvremove /dev/testvg/testlv
Do you really want to remove active logical volume "testlv"? [y/n]: y
Logical volume "testlv" successfully removed
You could explicitly deactivate the logical volume before removing it with the lvchange -an command,
in which case you would not see the prompt verifying whether you want to remove an active logical
volume.
5.4.13. Displaying Logical Volumes
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There are three commands you can use to display properties of LVM logical volumes: lvs, lvdisplay,
and lvscan.
The lvs command provides logical volume information in a configurable form, displaying one line per
logical volume. The lvs command provides a great deal of format control, and is useful for scripting. For
information on using the lvs command to customize your output, see Section 5.8, “Customized
Reporting for LVM”.
The lvdisplay command displays logical volume properties (such as size, layout, and mapping) in a
fixed format.
The following command shows the attributes of lvol2 in vg00. If snapshot logical volumes have been
created for this original logical volume, this command shows a list of all snapshot logical volumes and
their status (active or inactive) as well.
# lvdisplay -v /dev/vg00/lvol2
The lvscan command scans for all logical volumes in the system and lists them, as in the following
example.
# lvscan
ACTIVE
'/dev/vg0/gfslv' [1.46 GB] inherit
5.4.14. Growing Logical Volumes
To increase the size of a logical volume, use the lvextend command.
When you extend the logical volume, you can indicate how much you want to extend the volume, or how
large you want it to be after you extend it.
The following command extends the logical volume /dev/myvg/homevol to 12 gigabytes.
# lvextend -L12G /dev/myvg/homevol
lvextend -- extending logical volume "/dev/myvg/homevol" to 12 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
The following command adds another gigabyte to the logical volume /dev/myvg/homevol.
# lvextend -L+1G /dev/myvg/homevol
lvextend -- extending logical volume "/dev/myvg/homevol" to 13 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
As with the lvcreate command, you can use the -l argument of the lvextend command to specify
the number of extents by which to increase the size of the logical volume. You can also use this
argument to specify a percentage of the volume group, or a percentage of the remaining free space in the
volume group. The following command extends the logical volume called testlv to fill all of the
unallocated space in the volume group myvg.
# lvextend -l +100%FREE /dev/myvg/testlv
Extending logical volume testlv to 68.59 GB
Logical volume testlv successfully resized
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After you have extended the logical volume it is necessary to increase the file system size to match.
By default, most file system resizing tools will increase the size of the file system to be the size of the
underlying logical volume so you do not need to worry about specifying the same size for each of the two
commands.
5.4.14.1. Extending a Striped Volume
In order to increase the size of a striped logical volume, there must be enough free space on the
underlying physical volumes that make up the volume group to support the stripe. For example, if you
have a two-way stripe that that uses up an entire volume group, adding a single physical volume to the
volume group will not enable you to extend the stripe. Instead, you must add at least two physical
volumes to the volume group.
For example, consider a volume group vg that consists of two underlying physical volumes, as displayed
with the following vgs command.
# vgs
VG
vg
#PV #LV #SN Attr
VSize
VFree
2
0
0 wz--n- 271.31G 271.31G
You can create a stripe using the entire amount of space in the volume group.
# lvcreate -n stripe1 -L 271.31G -i 2 vg
Using default stripesize 64.00 KB
Rounding up size to full physical extent 271.31 GB
Logical volume "stripe1" created
# lvs -a -o +devices
LV
VG
Attr
LSize
Origin Snap% Move Log Copy%
stripe1 vg
-wi-a- 271.31G
/dev/sda1(0),/dev/sdb1(0)
Devices
Note that the volume group now has no more free space.
# vgs
VG
vg
#PV #LV #SN Attr
VSize
VFree
2
1
0 wz--n- 271.31G
0
The following command adds another physical volume to the volume group, which then has 135G of
additional space.
# vgextend vg /dev/sdc1
Volume group "vg" successfully extended
# vgs
VG
#PV #LV #SN Attr
VSize
VFree
vg
3
1
0 wz--n- 406.97G 135.66G
At this point you cannot extend the striped logical volume to the full size of the volume group, because
two underlying devices are needed in order to stripe the data.
# lvextend vg/stripe1 -L 406G
Using stripesize of last segment 64.00 KB
Extending logical volume stripe1 to 406.00 GB
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
Insufficient suitable allocatable extents for logical volume stripe1:
34480
more required
To extend the striped logical volume, add another physical volume and then extend the logical volume. In
this example, having added two physical volumes to the volume group we can extend the logical volume
to the full size of the volume group.
# vgextend vg /dev/sdd1
Volume group "vg" successfully extended
# vgs
VG
#PV #LV #SN Attr
VSize
VFree
vg
4
1
0 wz--n- 542.62G 271.31G
# lvextend vg/stripe1 -L 542G
Using stripesize of last segment 64.00 KB
Extending logical volume stripe1 to 542.00 GB
Logical volume stripe1 successfully resized
If you do not have enough underlying physical devices to extend the striped logical volume, it is possible
to extend the volume anyway if it does not matter that the extension is not striped, which may result in
uneven performance. When adding space to the logical volume, the default operation is to use the same
striping parameters of the last segment of the existing logical volume, but you can override those
parameters. The following example extends the existing striped logical volume to use the remaining free
space after the initial lvextend command fails.
# lvextend vg/stripe1 -L 406G
Using stripesize of last segment 64.00 KB
Extending logical volume stripe1 to 406.00 GB
Insufficient suitable allocatable extents for logical volume stripe1:
34480
more required
# lvextend -i1 -l+100%FREE vg/stripe1
5.4.14.2. Extending a Mirrored Volume
As of the Red Hat Enterprise Linux 6.3 release, it is possible to grow mirrored logical volumes with the
lvextend command without performing a synchronization of the new mirror regions.
If you specify the --nosync option when you create a mirrored logical volume with the lvcreate
command, the mirror regions are not synchronized when the mirror is created, as described in
Section 5.4.3, “Creating Mirrored Volumes”. If you later extend a mirror that you have created with the -nosync option, the mirror extensions are not synchronized at that time, either.
You can determine whether an existing logical volume was created with the --nosync option by using
the lvs command to display the volume's attributes. A logical volume will have an attribute bit 1 of "M" if
it is a mirrored volume that was created without an initial synchronization, and it will have an attribute bit
1 of "m" if it was created with initial synchronization.
The following command displays the attributes of a mirrored logical volume named lv that was created
without initial synchronization, showing attribute bit 1 as "M". Attribute bit 7 is "m", indicating a target type
of mirror. For information on the meaning of the attribute bits, see Table 5.4, “lvs Display Fields”.
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Logical Volume Manager Administration
# lvs vg
LV
VG
lv
vg
Attr
LSize Pool Origin Snap%
Mwi-a-m- 5.00g
Move Log
Copy% Convert
lv_mlog 100.00
If you grow this mirrored logical volume with the lvextend command, the mirror extension will not be
resynchronized.
If you created a mirrored logical volume without specifying the --nosync option of the lvcreate
command, you can grow the logical volume without resynchronizing the mirror by specifying the -nosync option of the lvextend command.
The following example extends a logical volume that was created without the --nosync option,
indicated that the mirror was synchronized when it was created. This example, however, specifies that
the mirror not be synchronized when the volume is extended. Note that the volume has an attribute of
"m", but after executing the lvextend commmand with the --nosync option the volume has an
attribute of "M".
# lvs vg
LV
VG
Attr
LSize Pool Origin Snap% Move Log
Copy%
Convert
lv
vg
mwi-a-m- 20.00m
lv_mlog 100.00
# lvextend -L +5G vg/lv --nosync
Extending 2 mirror images.
Extending logical volume lv to 5.02 GiB
Logical volume lv successfully resized
# lvs vg
LV
VG
Attr
LSize Pool Origin Snap% Move Log
Copy% Convert
lv
vg
Mwi-a-m- 5.02g
lv_mlog 100.00
If a mirror is inactive, it will not automatically skip synchronization when you extend the mirror, even if
you create the mirror with the --nosync option specified. Instead, you will be prompted whether to do a
full resync of the extended portion of the logical volume.
NOTE
If a mirror is performing recovery, you cannot extend the mirrored logical volume if you
created or extended the volume with the --nosync option specified. If you did not specify
the --nosync option, however, you can extend the mirror while it is recovering.
5.4.14.3. Extending a Logical Volume with the cling Allocation Policy
When extending an LVM volume, you can use the --alloc cling option of the lvextend command
to specify the cling allocation policy. This policy will choose space on the same physical volumes as the
last segment of the existing logical volume. If there is insufficient space on the physical volumes and a list
of tags is defined in the lvm.conf file, LVM will check whether any of the tags are attached to the
physical volumes and seek to match those physical volume tags between existing extents and new
extents.
For example, if you have logical volumes that are mirrored between two sites within a single volume
group, you can tag the physical volumes according to where they are situated by tagging the physical
volumes with @site1 and @site2 tags and specify the following line in the lvm.conf file:
cling_tag_list = [ "@site1", "@site2" ]
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For information on tagging physical volumes, see Appendix D, LVM Object Tags.
In the following example, the lvm.conf file has been modified to contain the following line:
cling_tag_list = [ "@A", "@B" ]
Also in this example, a volume group taft has been created that consists of the physical volumes
/dev/sdb1, /dev/sdc1, /dev/sdd1, /dev/sde1, /dev/sdf1, /dev/sdg1, and /dev/sdh1. These
physical volumes have been tagged with tags A, B, and C. The example does not use the C tag, but this
will show that LVM uses the tags to select which physical volumes to use for the mirror legs.
# pvs -a -o +pv_tags /dev/sd[bcdefgh]1
PV
VG
Fmt Attr PSize
PFree
/dev/sdb1 taft lvm2 a135.66g 135.66g
/dev/sdc1 taft lvm2 a135.66g 135.66g
/dev/sdd1 taft lvm2 a135.66g 135.66g
/dev/sde1 taft lvm2 a135.66g 135.66g
/dev/sdf1 taft lvm2 a135.66g 135.66g
/dev/sdg1 taft lvm2 a135.66g 135.66g
/dev/sdh1 taft lvm2 a135.66g 135.66g
PV Tags
A
B
B
C
C
A
A
The following command creates a 100GB mirrored volume from the volume group taft.
# lvcreate -m 1 -n mirror --nosync -L 100G taft
The following command shows which devices are used for the mirror legs and mirror log.
# lvs -a -o +devices
LV
VG
Attr
LSize
Log
Copy% Devices
mirror
taft
Mwi-a- 100.00g mirror_mlog 100.00
mirror_mimage_0(0),mirror_mimage_1(0)
[mirror_mimage_0] taft
iwi-ao 100.00g
/dev/sdb1(0)
[mirror_mimage_1] taft
iwi-ao 100.00g
/dev/sdc1(0)
[mirror_mlog]
taft
lwi-ao
4.00m
/dev/sdh1(0)
The following command extends the size of the mirrored volume, using the cling allocation policy to
indicate that the mirror legs should be extended using physical volumes with the same tag.
# lvextend --alloc cling -L +100G taft/mirror
Extending 2 mirror images.
Extending logical volume mirror to 200.00 GiB
Logical volume mirror successfully resized
The following display command shows that the mirror legs have been extended using physical volumes
with the same tag as the leg. Note that the physical volumes with a tag of C were ignored.
# lvs -a -o +devices
LV
VG
Attr
LSize
Log
Copy% Devices
mirror
taft
Mwi-a- 200.00g mirror_mlog 50.16
mirror_mimage_0(0),mirror_mimage_1(0)
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[mirror_mimage_0]
/dev/sdb1(0)
[mirror_mimage_0]
/dev/sdg1(0)
[mirror_mimage_1]
/dev/sdc1(0)
[mirror_mimage_1]
/dev/sdd1(0)
[mirror_mlog]
/dev/sdh1(0)
taft
Iwi-ao 200.00g
taft
Iwi-ao 200.00g
taft
Iwi-ao 200.00g
taft
Iwi-ao 200.00g
taft
lwi-ao
4.00m
5.4.15. Shrinking Logical Volumes
You can reduce the size of a logical volume with the lvreduce command.
NOTE
Shrinking is not supported on a GFS2 or XFS file system, so you cannot reduce the size
of a logical volume that contains a GFS2 or XFS file system.
If the logical volume you are reducing contains a file system, to prevent data loss you must ensure that
the file system is not using the space in the logical volume that is being reduced. For this reason, it is
recommended that you use the --resizefs option of the lvreduce command when the logical
volume contains a file system. When you use this option, the lvreduce command attempts to reduce
the file system before shrinking the logical voume. If shrinking the file sytem fails, as can occur if the file
system is full or the file system does not support shrinking, then the lvreduce command will fail and not
attempt to shrink the logical volume.

WARNING
In most cases, the lvreduce command warns about possible data loss and asks
for a confirmation. However, you should not rely on these confirmation prompts to
prevent data loss because in some cases you will not see these prompts, such as
when the logical volume is inactive or the --resizefs option is not used.
Note that using the --test option of the lvreduce command does not indicate
where the operation is safe, as this option does not check the file system or test the
file system resize.
The following command shrinks the logical volume lvol1 in volume group vg00 to be 64 megabytes. In
this example, lvol1 contains a file system, which this command resizes together with the logical
volume. This example shows the output to the command.
# lvreduce --resizefs -L 64M vg00/lvol1
fsck from util-linux 2.23.2
/dev/mapper/vg00-lvol1: clean, 11/25688 files, 8896/102400 blocks
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/mapper/vg00-lvol1 to 65536 (1k) blocks.
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The filesystem on /dev/mapper/vg00-lvol1 is now 65536 blocks long.
Size of logical volume vg00/lvol1 changed from 100.00 MiB (25 extents)
to 64.00 MiB (16 extents).
Logical volume vg00/lvol1 successfully resized.
Specifying the - sign before the resize value indicates that the value will be subtracted from the logical
volume's actual size. The following example shows the command you would use if, instead of shrinking a
logical volume to an absolute size of 64 megabytes, you wanted to shrink the volume by a value 64
megabytes.
# lvreduce --resizefs -L -64M vg00/lvol1
5.4.16. RAID Logical Volumes
As of the Red Hat Enterprise Linux 6.3 release, LVM supports RAID4/5/6 and a new implementation of
mirroring. The latest implementation of mirroring differs from the previous implementation of mirroring
(documented in Section 5.4.3, “Creating Mirrored Volumes”) in the following ways:
The segment type for the new implementation of mirroring is raid1. For the earlier
implementation, the segment type is mirror.
The new implementation of mirroring leverages MD software RAID, just as for the RAID 4/5/6
implementations.
The new implementation of mirroring maintains a fully redundant bitmap area for each mirror
image, which increases its fault handling capabilities. This means that there is no --mirrorlog
option or --corelog option for mirrors created with this segment type.
The new implementation of mirroring can handle transient failures.
Mirror images can be temporarily split from the array and merged back into the array later.
The new implementation of mirroring supports snapshots (as do the higher-level RAID
implementations).
The new RAID implementations are not cluster-aware. You cannot create an LVM RAID logical
volume in a clustered volume group.
For information on how failures are handled by the RAID logical volumes, see Section 5.4.16.8, “Setting a
RAID fault policy”.
The remainder of this section describes the following administrative tasks you can perform on LVM RAID
devices:
Section 5.4.16.1, “Creating a RAID Logical Volume”
Section 5.4.16.2, “Converting a Linear Device to a RAID Device”
Section 5.4.16.3, “Converting an LVM RAID1 Logical Volume to an LVM Linear Logical Volume”
Section 5.4.16.4, “Converting a Mirrored LVM Device to a RAID1 Device”
Section 5.4.16.5, “Changing the Number of Images in an Existing RAID1 Device”
Section 5.4.16.6, “Splitting off a RAID Image as a Separate Logical Volume”
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Section 5.4.16.7, “Splitting and Merging a RAID Image”
Section 5.4.16.8, “Setting a RAID fault policy”
Section 5.4.16.9, “Replacing a RAID device”
Section 5.4.16.10, “Scrubbing a RAID Logical Volume”
Section 5.4.16.11, “Controlling I/O Operations on a RAID1 Logical Volume”
5.4.16.1. Creating a RAID Logical Volume
To create a RAID logical volume, you specify a raid type as the --type argument of the lvcreate
command. Usually when you create a logical volume with the lvcreate command, the --type
argument is implicit. For example, when you specify the -i stripes argument, the lvcreate
command assumes the --type stripe option. When you specify the -m mirrors argument, the
lvcreate command assumes the --type mirror option. When you create a RAID logical volume,
however, you must explicitly specify the segment type you desire. The possible RAID segment types are
described in Table 5.1, “RAID Segment Types”.
Table 5.1. RAID Segment Types
Segment type
Description
raid1
RAID1 mirroring
raid4
RAID4 dedicated parity disk
raid5
Same as raid5_ls
raid5_la
RAID5 left asymmetric.
Rotating parity 0 with data continuation
raid5_ra
RAID5 right asymmetric.
Rotating parity N with data continuation
raid5_ls
RAID5 left symmetric.
Rotating parity 0 with data restart
raid5_rs
RAID5 right symmetric.
Rotating parity N with data restart
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Segment type
Description
raid6
Same as raid6_zr
raid6_zr
RAID6 zero restart
Rotating parity zero (left-to-right) with data restart
raid6_nr
RAID6 N restart
Rotating parity N (left-to-right) with data restart
raid6_nc
RAID6 N continue
Rotating parity N (left-to-right) with data continuation
raid10 (Red Hat
Enterprise Linux 6.4 and
later
Striped mirrors
Striping of mirror sets
For most users, specifying one of the five available primary types (raid1, raid4, raid5, raid6,
raid10) should be sufficient. For more information on the different algorithms used by RAID 5/6, see
chapter four of the Common RAID Disk Data Format Specification at
http://www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf.
When you create a RAID logical volume, LVM creates a metadata subvolume that is one extent in size
for every data or parity subvolume in the array. For example, creating a 2-way RAID1 array results in two
metadata subvolumes (lv_rmeta_0 and lv_rmeta_1) and two data subvolumes (lv_rimage_0 and
lv_rimage_1). Similarly, creating a 3-way stripe (plus 1 implicit parity device) RAID4 results in 4
metadata subvolumes (lv_rmeta_0, lv_rmeta_1, lv_rmeta_2, and lv_rmeta_3) and 4 data
subvolumes (lv_rimage_0, lv_rimage_1, lv_rimage_2, and lv_rimage_3).
The following command creates a 2-way RAID1 array named my_lv in the volume group my_vg that is
1G in size.
# lvcreate --type raid1 -m 1 -L 1G -n my_lv my_vg
You can create RAID1 arrays with different numbers of copies according to the value you specify for the
-m argument. Although the -m argument is the same argument used to specify the number of copies for
the previous mirror implementation, in this case you override the default segment type mirror by
explicitly setting the segment type as raid1. Similarly, you specify the number of stripes for a RAID 4/5/6
logical volume with the familiar -i argument, overriding the default segment type with the desired
RAID type. You can also specify the stripe size with the -I argument.
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NOTE
You can set the default mirror segment type to raid1 by changing
mirror_segtype_default in the lvm.conf file.
The following command creates a RAID5 array (3 stripes + 1 implicit parity drive) named my_lv in the
volume group my_vg that is 1G in size. Note that you specify the number of stripes just as you do for an
LVM striped volume; the correct number of parity drives is added automatically.
# lvcreate --type raid5 -i 3 -L 1G -n my_lv my_vg
The following command creates a RAID6 array (3 stripes + 2 implicit parity drives) named my_lv in the
volume group my_vg that is 1G in size.
# lvcreate --type raid6 -i 3 -L 1G -n my_lv my_vg
After you have created a RAID logical volume with LVM, you can activate, change, remove, display, and
use the volume just as you would any other LVM logical volume.
When you create RAID10 logical volumes, the background I/O required to initialize the logical volumes
with a sync operation can crowd out other I/O operations to LVM devices, such as updates to volume
group metadata, particularly when you are creating many RAID logical volumes. This can cause the
other LVM operations to slow down.
As of Red Hat Enterprise Linux 6.5, you can control the rate at which a RAID logical volume is initialized
by implementing recovery throttling. You control the rate at which sync operations are performed by
setting the minimum and maximum I/O rate for those operations with the --minrecoveryrate and -maxrecoveryrate options of the lvcreate command. You specify these options as follows.
--maxrecoveryrate Rate[bBsSkKmMgG]
Sets the maximum recovery rate for a RAID logical volume so that it will not crowd out nominal
I/O operations. The Rate is specified as an amount per second for each device in the array. If no
suffix is given, then kiB/sec/device is assumed. Setting the recovery rate to 0 means it will be
unbounded.
--minrecoveryrate Rate[bBsSkKmMgG]
Sets the minimum recovery rate for a RAID logical volume to ensure that I/O for sync operations
achieves a minimum throughput, even when heavy nominal I/O is present. The Rate is specified
as an amount per second for each device in the array. If no suffix is given, then kiB/sec/device is
assumed.
The following command creates a 2-way RAID10 array with 3 stripes that is 10G is size with a maximum
recovery rate of 128 kiB/sec/device. The array is named my_lv and is in the volume group my_vg.
lvcreate --type raid10 -i 2 -m 1 -L 10G --maxrecoveryrate 128 -n my_lv
my_vg
You can also specify minimum and maximum recovery rates for a RAID scrubbing operation. For
information on RAID scrubbing, see Section 5.4.16.10, “Scrubbing a RAID Logical Volume”.
5.4.16.2. Converting a Linear Device to a RAID Device
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You can convert an existing linear logical volume to a RAID device by using the --type argument of the
lvconvert command.
The following command converts the linear logical volume my_lv in volume group my_vg to a 2-way
RAID1 array.
# lvconvert --type raid1 -m 1 my_vg/my_lv
Since RAID logical volumes are composed of metadata and data subvolume pairs, when you convert a
linear device to a RAID1 array, a new metadata subvolume is created and associated with the original
logical volume on (one of) the same physical volumes that the linear volume is on. The additional images
are added in metadata/data subvolume pairs. For example, if the original device is as follows:
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
/dev/sde1(0)
After conversion to a 2-way RAID1 array the device contains the following data and metadata subvolume
pairs:
# lvconvert --type raid1 -m 1 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
6.25
my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sde1(0)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rmeta_0]
/dev/sde1(256)
[my_lv_rmeta_1]
/dev/sdf1(0)
If the metadata image that pairs with the original logical volume cannot be placed on the same physical
volume, the lvconvert will fail.
5.4.16.3. Converting an LVM RAID1 Logical Volume to an LVM Linear Logical Volume
You can convert an existing RAID1 LVM logical volume to an LVM linear logical volume with the
lvconvert command by specifying the -m0 argument. This removes all the RAID data subvolumes and
all the RAID metadata subvolumes that make up the RAID array, leaving the top-level RAID1 image as
the linear logical volume.
The following example displays an existing LVM RAID1 logical volume.
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
The following command converts the LVM RAID1 logical volume my_vg/my_lv to an LVM linear device.
# lvconvert -m0 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
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Logical Volume Manager Administration
my_lv
/dev/sde1(1)
When you convert an LVM RAID1 logical volume to an LVM linear volume, you can specify which
physical volumes to remove. The following example shows the layout of an LVM RAID1 logical volume
made up of two images: /dev/sda1 and /dev/sdb1. In this example, the lvconvert command
specifies that you want to remove /dev/sda1, leaving /dev/sdb1 as the physical volume that makes
up the linear device.
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sda1(1)
[my_lv_rimage_1]
/dev/sdb1(1)
[my_lv_rmeta_0]
/dev/sda1(0)
[my_lv_rmeta_1]
/dev/sdb1(0)
# lvconvert -m0 my_vg/my_lv /dev/sda1
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
/dev/sdb1(1)
5.4.16.4. Converting a Mirrored LVM Device to a RAID1 Device
You can convert an existing mirrored LVM device to a RAID1 LVM device with the lvconvert
command by specifying the --type raid1 argument. This renames the mirror subvolumes
(*_mimage_*) to RAID subvolumes (*_rimage_*). In addition, the mirror log is removed and metadata
subvolumes (*_rmeta_*) are created for the data subvolumes on the same physical volumes as the
corresponding data subvolumes.
The following example shows the layout of a mirrored logical volume my_vg/my_lv.
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
15.20 my_lv_mimage_0(0),my_lv_mimage_1(0)
[my_lv_mimage_0]
/dev/sde1(0)
[my_lv_mimage_1]
/dev/sdf1(0)
[my_lv_mlog]
/dev/sdd1(0)
The following command converts the mirrored logical volume my_vg/my_lv to a RAID1 logical volume.
# lvconvert --type raid1 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sde1(0)
[my_lv_rimage_1]
/dev/sdf1(0)
[my_lv_rmeta_0]
/dev/sde1(125)
[my_lv_rmeta_1]
/dev/sdf1(125)
5.4.16.5. Changing the Number of Images in an Existing RAID1 Device
You can change the number of images in an existing RAID1 array just as you can change the number of
images in the earlier implementation of LVM mirroring, by using the lvconvert command to specify the
number of additional metadata/data subvolume pairs to add or remove. For information on changing the
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
volume configuration in the earlier implementation of LVM mirroring, see Section 5.4.3.4, “Changing
Mirrored Volume Configuration”.
When you add images to a RAID1 device with the lvconvert command, you can specify the total
number of images for the resulting device, or you can specify how many images to add to the device.
You can also optionally specify on which physical volumes the new metadata/data image pairs will
reside.
Metadata subvolumes (named *_rmeta_*) always exist on the same physical devices as their data
subvolume counterparts *_rimage_*). The metadata/data subvolume pairs will not be created on the
same physical volumes as those from another metadata/data subvolume pair in the RAID array (unless
you specify --alloc anywhere).
The format for the command to add images to a RAID1 volume is as follows:
lvconvert -m new_absolute_count vg/lv [removable_PVs]
lvconvert -m +num_additional_images vg/lv [removable_PVs]
For example, the following display shows the LVM device my_vg/my_lv which is a 2-way RAID1 array:
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
6.25 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sde1(0)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rmeta_0]
/dev/sde1(256)
[my_lv_rmeta_1]
/dev/sdf1(0)
The following command converts the 2-way RAID1 device my_vg/my_lv to a 3-way RAID1 device:
# lvconvert -m 2 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
6.25
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sde1(0)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rimage_2]
/dev/sdg1(1)
[my_lv_rmeta_0]
/dev/sde1(256)
[my_lv_rmeta_1]
/dev/sdf1(0)
[my_lv_rmeta_2]
/dev/sdg1(0)
When you add an image to a RAID1 array, you can specify which physical volumes to use for the image.
The following command converts the 2-way RAID1 device my_vg/my_lv to a 3-way RAID1 device,
specifying that the physical volume /dev/sdd1 be used for the array:
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
56.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sda1(1)
[my_lv_rimage_1]
/dev/sdb1(1)
[my_lv_rmeta_0]
/dev/sda1(0)
[my_lv_rmeta_1]
/dev/sdb1(0)
# lvconvert -m 2 my_vg/my_lv /dev/sdd1
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Logical Volume Manager Administration
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
28.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sda1(1)
[my_lv_rimage_1]
/dev/sdb1(1)
[my_lv_rimage_2]
/dev/sdd1(1)
[my_lv_rmeta_0]
/dev/sda1(0)
[my_lv_rmeta_1]
/dev/sdb1(0)
[my_lv_rmeta_2]
/dev/sdd1(0)
To remove images from a RAID1 array, use the following command. When you remove images from a
RAID1 device with the lvconvert command, you can specify the total number of images for the
resulting device, or you can specify how many images to remove from the device. You can also
optionally specify the physical volumes from which to remove the device.
lvconvert -m new_absolute_count vg/lv [removable_PVs]
lvconvert -m -num_fewer_images vg/lv [removable_PVs]
Additionally, when an image and its associated metadata subvolume volume are removed, any highernumbered images will be shifted down to fill the slot. If you remove lv_rimage_1 from a 3-way RAID1
array that consists of lv_rimage_0, lv_rimage_1, and lv_rimage_2, this results in a RAID1 array
that consists of lv_rimage_0 and lv_rimage_1. The subvolume lv_rimage_2 will be renamed and
take over the empty slot, becoming lv_rimage_1.
The following example shows the layout of a 3-way RAID1 logical volume my_vg/my_lv.
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rimage_2]
/dev/sdg1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
[my_lv_rmeta_2]
/dev/sdg1(0)
The following command converts the 3-way RAID1 logical volume into a 2-way RAID1 logical volume.
# lvconvert -m1 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
The following command converts the 3-way RAID1 logical volume into a 2-way RAID1 logical volume,
specifying the physical volume that contains the image to remove as /dev/sde1.
# lvconvert -m1 my_vg/my_lv /dev/sde1
# lvs -a -o name,copy_percent,devices my_vg
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
LV
Copy%
my_lv
100.00
[my_lv_rimage_0]
[my_lv_rimage_1]
[my_lv_rmeta_0]
[my_lv_rmeta_1]
Devices
my_lv_rimage_0(0),my_lv_rimage_1(0)
/dev/sdf1(1)
/dev/sdg1(1)
/dev/sdf1(0)
/dev/sdg1(0)
5.4.16.6. Splitting off a RAID Image as a Separate Logical Volume
You can split off an image of a RAID logical volume to form a new logical volume. The procedure for
splitting off a RAID image is the same as the procedure for splitting off a redundant image of a mirrored
logical volume, as described in Section 5.4.3.2, “Splitting Off a Redundant Image of a Mirrored Logical
Volume”.
The format of the command to split off a RAID image is as follows:
lvconvert --splitmirrors count -n splitname vg/lv [removable_PVs]
Just as when you are removing a RAID images from an existing RAID1 logical volume (as described in
Section 5.4.16.5, “Changing the Number of Images in an Existing RAID1 Device”), when you remove a
RAID data subvolume (and its associated metadata subvolume) from the middle of the device, any
higher numbered images will be shifted down to fill the slot. The index numbers on the logical volumes
that make up a RAID array will thus be an unbroken sequence of integers.
NOTE
You cannot split off a RAID image if the RAID1 array is not yet in sync.
The following example splits a 2-way RAID1 logical volume, my_lv, into two linear logical volumes,
my_lv and new.
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
12.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
# lvconvert --splitmirror 1 -n new my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
/dev/sde1(1)
new
/dev/sdf1(1)
The following example splits a 3-way RAID1 logical volume, my_lv, into a 2-way RAID1 logical volume,
my_lv, and a linear logical volume, new
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
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Logical Volume Manager Administration
[my_lv_rimage_2]
/dev/sdg1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
[my_lv_rmeta_2]
/dev/sdg1(0)
# lvconvert --splitmirror 1 -n new my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
new
/dev/sdg1(1)
5.4.16.7. Splitting and Merging a RAID Image
You can temporarily split off an image of a RAID1 array for read-only use while keeping track of any
changes by using the --trackchanges argument in conjunction with the --splitmirrors argument
of the lvconvert command. This allows you to merge the image back into the array at a later time while
resyncing only those portions of the array that have changed since the image was split.
The format for the lvconvert command to split off a RAID image is as follows.
lvconvert --splitmirrors count --trackchanges vg/lv [removable_PVs]
When you split off a RAID image with the --trackchanges argument, you can specify which image to
split but you cannot change the name of the volume being split. In addition, the resulting volumes have
the following constraints.
The new volume you create is read-only.
You cannot resize the new volume.
You cannot rename the remaining array.
You cannot resize the remaining array.
You can activate the new volume and the remaining array independently.
You can merge an image that was split off with the --trackchanges argument specified by executing
a subsequent lvconvert command with the --merge argument. When you merge the image, only the
portions of the array that have changed since the image was split are resynced.
The format for the lvconvert command to merge a RAID image is as follows.
lvconvert --merge raid_image
The following example creates a RAID1 logical volume and then splits off an image from that volume
while tracking changes to the remaining array.
# lvcreate --type raid1 -m2 -L1G -n my_lv .vg
Logical volume "my_lv" created
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sdb1(1)
[my_lv_rimage_1]
/dev/sdc1(1)
[my_lv_rimage_2]
/dev/sdd1(1)
[my_lv_rmeta_0]
/dev/sdb1(0)
[my_lv_rmeta_1]
/dev/sdc1(0)
[my_lv_rmeta_2]
/dev/sdd1(0)
# lvconvert --splitmirrors 1 --trackchanges my_vg/my_lv
my_lv_rimage_2 split from my_lv for read-only purposes.
Use 'lvconvert --merge my_vg/my_lv_rimage_2' to merge back into my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sdb1(1)
[my_lv_rimage_1]
/dev/sdc1(1)
my_lv_rimage_2
/dev/sdd1(1)
[my_lv_rmeta_0]
/dev/sdb1(0)
[my_lv_rmeta_1]
/dev/sdc1(0)
[my_lv_rmeta_2]
/dev/sdd1(0)
The following example splits off an image from a RAID1 volume while tracking changes to the remaining
array, then merges the volume back into the array.
# lvconvert --splitmirrors 1 --trackchanges my_vg/my_lv
lv_rimage_1 split from my_lv for read-only purposes.
Use 'lvconvert --merge my_vg/my_lv_rimage_1' to merge back into my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sdc1(1)
my_lv_rimage_1
/dev/sdd1(1)
[my_lv_rmeta_0]
/dev/sdc1(0)
[my_lv_rmeta_1]
/dev/sdd1(0)
# lvconvert --merge my_vg/my_lv_rimage_1
my_vg/my_lv_rimage_1 successfully merged back into my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sdc1(1)
[my_lv_rimage_1]
/dev/sdd1(1)
[my_lv_rmeta_0]
/dev/sdc1(0)
[my_lv_rmeta_1]
/dev/sdd1(0)
Once you have split off an image from a RAID1 volume, you can make the split permanent by issuing a
second lvconvert --splitmirrors command, repeating the initial lvconvert command that split
the image without specifying the --trackchanges argument. This breaks the link that the -trackchanges argument created.
After you have split an image with the --trackchanges argument, you cannot issue a subsequent
lvconvert --splitmirrors command on that array unless your intent is to permanently split the
image being tracked.
The following sequence of commands splits an image and tracks the image and then permanently splits
off the image being tracked.
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Logical Volume Manager Administration
# lvconvert --splitmirrors 1 --trackchanges my_vg/my_lv
my_lv_rimage_1 split from my_lv for read-only purposes.
Use 'lvconvert --merge my_vg/my_lv_rimage_1' to merge back into my_lv
# lvconvert --splitmirrors 1 -n new my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
/dev/sdc1(1)
new
/dev/sdd1(1)
Note, however, that the following sequence of commands will fail.
# lvconvert --splitmirrors 1 --trackchanges my_vg/my_lv
my_lv_rimage_1 split from my_lv for read-only purposes.
Use 'lvconvert --merge my_vg/my_lv_rimage_1' to merge back into my_lv
# lvconvert --splitmirrors 1 --trackchanges my_vg/my_lv
Cannot track more than one split image at a time
Similarly, the following sequence of commands will fail as well, since the split image is not the image
being tracked.
# lvconvert --splitmirrors 1 --trackchanges my_vg/my_lv
my_lv_rimage_1 split from my_lv for read-only purposes.
Use 'lvconvert --merge my_vg/my_lv_rimage_1' to merge back into my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sdc1(1)
my_lv_rimage_1
/dev/sdd1(1)
[my_lv_rmeta_0]
/dev/sdc1(0)
[my_lv_rmeta_1]
/dev/sdd1(0)
# lvconvert --splitmirrors 1 -n new my_vg/my_lv /dev/sdc1
Unable to split additional image from my_lv while tracking changes for
my_lv_rimage_1
5.4.16.8. Setting a RAID fault policy
LVM RAID handles device failures in an automatic fashion based on the preferences defined by the
raid_fault_policy field in the lvm.conf file.
If the raid_fault_policy field is set to allocate, the system will attempt to replace the
failed device with a spare device from the volume group. If there is no available spare device,
this will be reported to the system log.
If the raid_fault_policy field is set to warn, the system will produce a warning and the log
will indicate that a device has failed. This allows the user to determine the course of action to
take.
As long as there are enough devices remaining to support usability, the RAID logical volume will
continue to operate.
5.4.16.8.1. The allocate RAID Fault Policy
In the following example, the raid_fault_policy field has been set to allocate in the lvm.conf
file. The RAID logical volume is laid out as follows.
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rimage_2]
/dev/sdg1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
[my_lv_rmeta_2]
/dev/sdg1(0)
If the /dev/sde device fails, the system log will display error messages.
# grep lvm /var/log/messages
Jan 17 15:57:18 bp-01 lvm[8599]: Device #0 of raid1 array, my_vg-my_lv,
has failed.
Jan 17 15:57:18 bp-01 lvm[8599]: /dev/sde1: read failed after 0 of 2048 at
250994294784: Input/output error
Jan 17 15:57:18 bp-01 lvm[8599]: /dev/sde1: read failed after 0 of 2048 at
250994376704: Input/output error
Jan 17 15:57:18 bp-01 lvm[8599]: /dev/sde1: read failed after 0 of 2048 at
0:
Input/output error
Jan 17 15:57:18 bp-01 lvm[8599]: /dev/sde1: read failed after 0 of 2048 at
4096: Input/output error
Jan 17 15:57:19 bp-01 lvm[8599]: Couldn't find device with uuid
3lugiV-3eSP-AFAR-sdrP-H20O-wM2M-qdMANy.
Jan 17 15:57:27 bp-01 lvm[8599]: raid1 array, my_vg-my_lv, is not in-sync.
Jan 17 15:57:36 bp-01 lvm[8599]: raid1 array, my_vg-my_lv, is now in-sync.
Since the raid_fault_policy field has been set to allocate, the failed device is replaced with a
new device from the volume group.
# lvs -a -o name,copy_percent,devices vg
Couldn't find device with uuid 3lugiV-3eSP-AFAR-sdrP-H20O-wM2M-qdMANy.
LV
Copy% Devices
lv
100.00 lv_rimage_0(0),lv_rimage_1(0),lv_rimage_2(0)
[lv_rimage_0]
/dev/sdh1(1)
[lv_rimage_1]
/dev/sdf1(1)
[lv_rimage_2]
/dev/sdg1(1)
[lv_rmeta_0]
/dev/sdh1(0)
[lv_rmeta_1]
/dev/sdf1(0)
[lv_rmeta_2]
/dev/sdg1(0)
Note that even though the failed device has been replaced, the display still indicates that LVM could not
find the failed device. This is because, although the failed device has been removed from the RAID
logical volume, the failed device has not yet been removed from the volume group. To remove the failed
device from the volume group, you can execute vgreduce --removemissing VG.
If the raid_fault_policy has been set to allocate but there are no spare devices, the allocation
will fail, leaving the logical volume as it is. If the allocation fails, you have the option of fixing the drive,
then deactivating and activating the logical volume, as described in Section 5.4.16.8.2, “The warn RAID
Fault Policy”. Alternately, you can replace the failed device, as described in Section 5.4.16.9, “Replacing
a RAID device”.
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Logical Volume Manager Administration
5.4.16.8.2. The warn RAID Fault Policy
In the following example, the raid_fault_policy field has been set to warn in the lvm.conf file.
The RAID logical volume is laid out as follows.
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sdh1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rimage_2]
/dev/sdg1(1)
[my_lv_rmeta_0]
/dev/sdh1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
[my_lv_rmeta_2]
/dev/sdg1(0)
If the /dev/sdh device fails, the system log will display error messages. In this case, however, LVM will
not automatically attempt to repair the RAID device by replacing one of the images. Instead, if the device
has failed you can replace the device with the --repair argument of the lvconvert command, as
shown below.
# lvconvert --repair my_vg/my_lv
/dev/sdh1: read failed after 0 of 2048 at 250994294784: Input/output
error
/dev/sdh1: read failed after 0 of 2048 at 250994376704: Input/output
error
/dev/sdh1: read failed after 0 of 2048 at 0: Input/output error
/dev/sdh1: read failed after 0 of 2048 at 4096: Input/output error
Couldn't find device with uuid fbI0YO-GX7x-firU-Vy5o-vzwx-vAKZ-feRxfF.
Attempt to replace failed RAID images (requires full device resync)?
[y/n]: y
# lvs -a -o name,copy_percent,devices my_vg
Couldn't find device with uuid fbI0YO-GX7x-firU-Vy5o-vzwx-vAKZ-feRxfF.
LV
Copy% Devices
my_lv
64.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sde1(1)
[my_lv_rimage_1]
/dev/sdf1(1)
[my_lv_rimage_2]
/dev/sdg1(1)
[my_lv_rmeta_0]
/dev/sde1(0)
[my_lv_rmeta_1]
/dev/sdf1(0)
[my_lv_rmeta_2]
/dev/sdg1(0)
Note that even though the failed device has been replaced, the display still indicates that LVM could not
find the failed device. This is because, although the failed device has been removed from the RAID
logical volume, the failed device has not yet been removed from the volume group. To remove the failed
device from the volume group, you can execute vgreduce --removemissing VG.
If the device failure is a transient failure or you are able to repair the device that failed, as of Red Hat
Enterprise Linux release 6.5 you can initiate recovery of the failed device with the --refresh option of
the lvchange command. Previously it was necessary to deactivate and then activate the logical volume.
The following command refreshes a logical volume.
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# lvchange --refresh my_vg/my_lv
5.4.16.9. Replacing a RAID device
RAID is not like traditional LVM mirroring. LVM mirroring required failed devices to be removed or the
mirrored logical volume would hang. RAID arrays can keep on running with failed devices. In fact, for
RAID types other than RAID1, removing a device would mean converting to a lower level RAID (for
example, from RAID6 to RAID5, or from RAID4 or RAID5 to RAID0). Therefore, rather than removing a
failed device unconditionally and potentially allocating a replacement, LVM allows you to replace a
device in a RAID volume in a one-step solution by using the --replace argument of the lvconvert
command.
The format for the lvconvert --replace is as follows.
lvconvert --replace dev_to_remove vg/lv [possible_replacements]
The following example creates a RAID1 logical volume and then replaces a device in that volume.
# lvcreate --type raid1 -m2 -L 1G -n my_lv my_vg
Logical volume "my_lv" created
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sdb1(1)
[my_lv_rimage_1]
/dev/sdb2(1)
[my_lv_rimage_2]
/dev/sdc1(1)
[my_lv_rmeta_0]
/dev/sdb1(0)
[my_lv_rmeta_1]
/dev/sdb2(0)
[my_lv_rmeta_2]
/dev/sdc1(0)
# lvconvert --replace /dev/sdb2 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
37.50
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sdb1(1)
[my_lv_rimage_1]
/dev/sdc2(1)
[my_lv_rimage_2]
/dev/sdc1(1)
[my_lv_rmeta_0]
/dev/sdb1(0)
[my_lv_rmeta_1]
/dev/sdc2(0)
[my_lv_rmeta_2]
/dev/sdc1(0)
The following example creates a RAID1 logical volume and then replaces a device in that volume,
specifying which physical volume to use for the replacement.
# lvcreate --type raid1 -m1 -L 100 -n my_lv my_vg
Logical volume "my_lv" created
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sda1(1)
[my_lv_rimage_1]
/dev/sdb1(1)
[my_lv_rmeta_0]
/dev/sda1(0)
[my_lv_rmeta_1]
/dev/sdb1(0)
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# pvs
PV
VG
Fmt Attr PSize
PFree
/dev/sda1
my_vg
lvm2 a-- 1020.00m 916.00m
/dev/sdb1
my_vg
lvm2 a-- 1020.00m 916.00m
/dev/sdc1
my_vg
lvm2 a-- 1020.00m 1020.00m
/dev/sdd1
my_vg
lvm2 a-- 1020.00m 1020.00m
# lvconvert --replace /dev/sdb1 my_vg/my_lv /dev/sdd1
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
28.00 my_lv_rimage_0(0),my_lv_rimage_1(0)
[my_lv_rimage_0]
/dev/sda1(1)
[my_lv_rimage_1]
/dev/sdd1(1)
[my_lv_rmeta_0]
/dev/sda1(0)
[my_lv_rmeta_1]
/dev/sdd1(0)
You can replace more than one RAID device at a time by specifying multiple replace arguments, as in
the following example.
# lvcreate --type raid1 -m 2 -L 100 -n my_lv my_vg
Logical volume "my_lv" created
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
100.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sda1(1)
[my_lv_rimage_1]
/dev/sdb1(1)
[my_lv_rimage_2]
/dev/sdc1(1)
[my_lv_rmeta_0]
/dev/sda1(0)
[my_lv_rmeta_1]
/dev/sdb1(0)
[my_lv_rmeta_2]
/dev/sdc1(0)
# lvconvert --replace /dev/sdb1 --replace /dev/sdc1 my_vg/my_lv
# lvs -a -o name,copy_percent,devices my_vg
LV
Copy% Devices
my_lv
60.00
my_lv_rimage_0(0),my_lv_rimage_1(0),my_lv_rimage_2(0)
[my_lv_rimage_0]
/dev/sda1(1)
[my_lv_rimage_1]
/dev/sdd1(1)
[my_lv_rimage_2]
/dev/sde1(1)
[my_lv_rmeta_0]
/dev/sda1(0)
[my_lv_rmeta_1]
/dev/sdd1(0)
[my_lv_rmeta_2]
/dev/sde1(0)
NOTE
When you specify a replacement drive using the lvconvert --replace command, the
replacement drives should never be allocated from extra space on drives already used in
the array. For example, lv_rimage_0 and lv_rimage_1 should not be located on the
same physical volume.
5.4.16.10. Scrubbing a RAID Logical Volume
As of the Red Hat Enterprise Linux 6.5 release, LVM provides scrubbing support for RAID logical
volumes. RAID scrubbing is the process of reading all the data and parity blocks in an array and checking
to see whether they are coherent.
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You initiate a RAID scrubbing operation with the --syncaction option of the lvchange command.
You specify either a check or repair operation. A check operation goes over the array and records
the number of discrepancies in the array but does not repair them. A repair operation corrects the
discrepancies as it finds them.
The format of the command to scrub a RAID logical volume is as follows:
lvchange --syncaction {check|repair} vg/raid_lv
NOTE
The lvchange --syncaction repair vg/raid_lv operation does not perform the
same function as the lvconvert --repair vg/raid_lv operation. The lvchange
--syncaction repair operation initiates a background synchronization operation on
the array, while the lvconvert --repair operation is designed to repair/replace failed
devices in a mirror or RAID logical volume.
In support of the new RAID scrubbing operation, the lvs command now supports two new printable
fields: raid_sync_action and raid_mismatch_count. These fields are not printed by default. To
display these fields you specify them with the -o parameter of the lvs, as follows.
lvs -o +raid_sync_action,raid_mismatch_count vg/lv
The raid_sync_action field displays the current synchronization operation that the raid volume is
performing. It can be one of the following values:
idle: All sync operations complete (doing nothing)
resync: Initializing an array or recovering after a machine failure
recover: Replacing a device in the array
check: Looking for array inconsistencies
repair: Looking for and repairing inconsistencies
The raid_mismatch_count field displays the number of discrepancies found during a check
operation.
The Cpy%Sync field of the lvs command now prints the progress of any of the raid_sync_action
operations, including check and repair.
The lv_attr field of the lvs display now provides additional indicators in support of the RAID
scrubbing operation. Bit 9 of this field displays the health of the logical volume, and it now supports the
following indicators.
(m)ismatches indicates that there are discrepancies in a RAID logical volume. This character is
shown after a scrubbing operation has detected that portions of the RAID are not coherent.
(r)efresh indicates that a device in a RAID array has suffered a failure and the kernel regards it
as failed, even though LVM can read the device label and considers the device to be
operational. The logical should be (r)efreshed to notify the kernel that the device is now available,
or the device should be (r)eplaced if it is suspected of having failed.
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For information on the lvs command, see Section 5.8.2, “Object Selection”.
When you perform a RAID scrubbing operation, the background I/O required by the sync operations can
crowd out other I/O operations to LVM devices, such as updates to volume group metadata. This can
cause the other LVM operations to slow down. You can control the rate at which the RAID logical volume
is scrubbed by implementing recovery throttling.
You control the rate at which sync operations are performed by setting the minimum and maximum I/O
rate for those operations with the --minrecoveryrate and --maxrecoveryrate options of the
lvchange command. You specify these options as follows.
--maxrecoveryrate Rate[bBsSkKmMgG]
Sets the maximum recovery rate for a RAID logical volume so that it will not crowd out nominal
I/O operations. The Rate is specified as an amount per second for each device in the array. If no
suffix is given, then kiB/sec/device is assumed. Setting the recovery rate to 0 means it will be
unbounded.
--minrecoveryrate Rate[bBsSkKmMgG]
Sets the minimum recovery rate for a RAID logical volume to ensure that I/O for sync operations
achieves a minimum throughput, even when heavy nominal I/O is present. The Rate is specified
as an amount per second for each device in the array. If no suffix is given, then kiB/sec/device is
assumed.
5.4.16.11. Controlling I/O Operations on a RAID1 Logical Volume
As of the Red Hat Enterprise Linux release 6.5, you can control the I/O operations for a device in a
RAID1 logical volume by using the --writemostly and --writebehind parameters of the
lvchange command. The format for using these parameters is as follows.
--[raid]writemostly PhysicalVolume[:{t|y|n}]
Marks a device in a RAID1 logical volume as write-mostly. All reads to these drives will be
avoided unless necessary. Setting this parameter keeps the number of I/O operations to the
drive to a minimum. The default behavior is to set the write-mostly attribute for the specified
physical volume in the logical volume. It is possible to remove the write-mostly flag by
appending :n to the physical volume or to toggle the value by specifying :t. The -writemostly argument can be specified more than one time in a single command, making it
possible to toggle the write-mostly attributes for all the physical volumes in a logical volume at
once.
--[raid]writebehind IOCount
Specifies the maximum number of outstanding writes that are allowed to devices in a RAID1
logical volume that are marked as write-mostly. Once this value is exceeded, writes become
synchronous, causing all writes to the constituent devices to complete before the array signals
the write has completed. Setting the value to zero clears the preference and allows the system to
choose the value arbitrarily.
5.4.17. Controlling Logical Volume Activation
You can flag a logical volume to be skipped during normal activation commands with the -k or -setactivationskip {y|n} option of the lvcreate or lvchange command. This flag is not applied
during deactivation.
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You can determine whether this flag is set for a logical volume with the lvs command, which displays
the k attribute as in the following example.
# lvs vg/thin1s1
LV
VG Attr
LSize Pool Origin
thin1s1
vg Vwi---tz-k 1.00t pool0 thin1
By default, thin snapshot volumes are flagged for activation skip. You can activate a logical volume with
the k attribute set by using the -K or --ignoreactivationskip option in addition to the standard ay or --activate y option.
The following command activates a thin snapshot logical volume.
# lvchange -ay -K VG/SnapLV
The persistent "activation skip" flag can be turned off when the logical volume is created by specifying
the -kn or --setactivationskip n option of the lvcreate command. You can turn the flag off for
an existing logical volume by specifying the -kn or --setactivationskip n option of the lvchange
command. You can turn the flag on again with the -ky or --setactivationskip y option.
The following command creates a snapshot logical volume without the activation skip flag
# lvcreate --type thin -n SnapLV -kn -s ThinLV --thinpool VG/ThinPoolLV
The following command removes the activation skip flag from a snapshot logical volume.
# lvchange -kn VG/SnapLV
You can control the default activation skip setting with the auto_set_activation_skip setting in the
/etc/lvm/lvm.conf file.
5.5. CONTROLLING LVM DEVICE SCANS WITH FILTERS
At startup, the vgscan command is run to scan the block devices on the system looking for LVM labels,
to determine which of them are physical volumes and to read the metadata and build up a list of volume
groups. The names of the physical volumes are stored in the LVM cache file of each node in the system,
/etc/lvm/cache/.cache. Subsequent commands may read that file to avoiding rescanning.
You can control which devices LVM scans by setting up filters in the lvm.conf configuration file. The
filters in the lvm.conf file consist of a series of simple regular expressions that get applied to the device
names that are in the /dev directory to decide whether to accept or reject each block device found.
The following examples show the use of filters to control which devices LVM scans. Note that some of
these examples do not necessarily represent best practice, as the regular expressions are matched
freely against the complete pathname. For example, a/loop/ is equivalent to a/.*loop.*/ and would
match /dev/solooperation/lvol1.
The following filter adds all discovered devices, which is the default behavior as there is no filter
configured in the configuration file:
filter = [ "a/.*/" ]
The following filter removes the cdrom device in order to avoid delays if the drive contains no media:
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filter = [ "r|/dev/cdrom|" ]
The following filter adds all loop and removes all other block devices:
filter = [ "a/loop.*/", "r/.*/" ]
The following filter adds all loop and IDE and removes all other block devices:
filter =[ "a|loop.*|", "a|/dev/hd.*|", "r|.*|" ]
The following filter adds just partition 8 on the first IDE drive and removes all other block devices:
filter = [ "a|^/dev/hda8$|", "r/.*/" ]
NOTE
When the lvmetad daemon is running, the filter = setting in the
/etc/lvm/lvm.conf file does not apply when you execute the pvscan --cache
device command. To filter devices, you need to use the global_filter = setting.
Devices that fail the global filter are not opened by LVM and are never scanned. You may
need to use a global filter, for example, when you use LVM devices in VMs and you do
not want the contents of the devices in the VMs to be scanned by the physical host.
For more information on the lvm.conf file, see Appendix B, The LVM Configuration Files and the
lvm.conf(5) man page.
5.6. ONLINE DATA RELOCATION
You can move data while the system is in use with the pvmove command.
The pvmove command breaks up the data to be moved into sections and creates a temporary mirror to
move each section. For more information on the operation of the pvmove command, see the pvmove(8)
man page.
NOTE
In order to perform a pvmove operation in a cluster, you should ensure that the cmirror
package is installed and the cmirrord service is running.
The following command moves all allocated space off the physical volume /dev/sdc1 to other free
physical volumes in the volume group:
# pvmove /dev/sdc1
The following command moves just the extents of the logical volume MyLV.
# pvmove -n MyLV /dev/sdc1
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Since the pvmove command can take a long time to execute, you may want to run the command in the
background to avoid display of progress updates in the foreground. The following command moves all
extents allocated to the physical volume /dev/sdc1 over to /dev/sdf1 in the background.
# pvmove -b /dev/sdc1 /dev/sdf1
The following command reports the progress of the move as a percentage at five second intervals.
# pvmove -i5 /dev/sdd1
5.7. ACTIVATING LOGICAL VOLUMES ON INDIVIDUAL NODES IN A
CLUSTER
If you have LVM installed in a cluster environment, you may at times need to activate logical volumes
exclusively on one node.
To activate logical volumes exclusively on one node, use the lvchange -aey command. Alternatively,
you can use lvchange -aly command to activate logical volumes only on the local node but not
exclusively. You can later activate them on additional nodes concurrently.
You can also activate logical volumes on individual nodes by using LVM tags, which are described in
Appendix D, LVM Object Tags. You can also specify activation of nodes in the configuration file, which is
described in Appendix B, The LVM Configuration Files.
5.8. CUSTOMIZED REPORTING FOR LVM
You can produce concise and customizable reports of LVM objects with the pvs, lvs, and vgs
commands. The reports that these commands generate include one line of output for each object. Each
line contains an ordered list of fields of properties related to the object. There are five ways to select the
objects to be reported: by physical volume, volume group, logical volume, physical volume segment, and
logical volume segment.
The following sections provide:
A summary of command arguments you can use to control the format of the generated report.
A list of the fields you can select for each LVM object.
A summary of command arguments you can use to sort the generated report.
Instructions for specifying the units of the report output.
5.8.1. Format Control
Whether you use the pvs, lvs, or vgs command determines the default set of fields displayed and the
sort order. You can control the output of these commands with the following arguments:
You can change what fields are displayed to something other than the default by using the -o
argument. For example, the following output is the default display for the pvs command (which
displays information about physical volumes).
# pvs
PV
VG
Fmt
Attr PSize
PFree
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Logical Volume Manager Administration
/dev/sdb1
/dev/sdc1
/dev/sdd1
new_vg lvm2 anew_vg lvm2 anew_vg lvm2 a-
17.14G 17.14G
17.14G 17.09G
17.14G 17.14G
The following command displays only the physical volume name and size.
# pvs -o pv_name,pv_size
PV
PSize
/dev/sdb1 17.14G
/dev/sdc1 17.14G
/dev/sdd1 17.14G
You can append a field to the output with the plus sign (+), which is used in combination with the
-o argument.
The following example displays the UUID of the physical volume in addition to the default fields.
# pvs -o +pv_uuid
PV
VG
/dev/sdb1 new_vg
M7iv-6XqA-dqGeXY
/dev/sdc1 new_vg
01S9-X08M-mcpsVe
/dev/sdd1 new_vg
0RZ3-0dGW-UqkCS
Fmt Attr PSize PFree PV UUID
lvm2 a17.14G 17.14G onFF2w-1fLC-ughJ-D9eBlvm2 a-
17.14G 17.09G Joqlch-yWSj-kuEn-IdwM-
lvm2 a-
17.14G 17.14G yvfvZK-Cf31-j75k-dECm-
Adding the -v argument to a command includes some extra fields. For example, the pvs -v
command will display the DevSize and PV UUID fields in addition to the default fields.
# pvs -v
Scanning for physical volume names
PV
VG
Fmt Attr PSize PFree DevSize PV UUID
/dev/sdb1 new_vg lvm2 a17.14G 17.14G 17.14G onFF2w-1fLCughJ-D9eB-M7iv-6XqA-dqGeXY
/dev/sdc1 new_vg lvm2 a17.14G 17.09G 17.14G Joqlch-yWSjkuEn-IdwM-01S9-XO8M-mcpsVe
/dev/sdd1 new_vg lvm2 a17.14G 17.14G 17.14G yvfvZK-Cf31j75k-dECm-0RZ3-0dGW-tUqkCS
The --noheadings argument suppresses the headings line. This can be useful for writing
scripts.
The following example uses the --noheadings argument in combination with the pv_name
argument, which will generate a list of all physical volumes.
# pvs --noheadings -o pv_name
/dev/sdb1
/dev/sdc1
/dev/sdd1
The --separator separator argument uses separator to separate each field.
The following example separates the default output fields of the pvs command with an equals
sign (=).
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
# pvs --separator =
PV=VG=Fmt=Attr=PSize=PFree
/dev/sdb1=new_vg=lvm2=a-=17.14G=17.14G
/dev/sdc1=new_vg=lvm2=a-=17.14G=17.09G
/dev/sdd1=new_vg=lvm2=a-=17.14G=17.14G
To keep the fields aligned when using the separator argument, use the separator argument
in conjunction with the --aligned argument.
# pvs --separator = --aligned
PV
=VG
=Fmt =Attr=PSize =PFree
/dev/sdb1 =new_vg=lvm2=a- =17.14G=17.14G
/dev/sdc1 =new_vg=lvm2=a- =17.14G=17.09G
/dev/sdd1 =new_vg=lvm2=a- =17.14G=17.14G
You can use the -P argument of the lvs or vgs command to display information about a failed volume
that would otherwise not appear in the output. For information on the output this argument yields, see
Section 7.2, “Displaying Information on Failed Devices”.
For a full listing of display arguments, see the pvs(8), vgs(8) and lvs(8) man pages.
Volume group fields can be mixed with either physical volume (and physical volume segment) fields or
with logical volume (and logical volume segment) fields, but physical volume and logical volume fields
cannot be mixed. For example, the following command will display one line of output for each physical
volume.
# vgs -o +pv_name
VG
#PV #LV #SN Attr
VSize VFree
new_vg
3
1
0 wz--n- 51.42G 51.37G
new_vg
3
1
0 wz--n- 51.42G 51.37G
new_vg
3
1
0 wz--n- 51.42G 51.37G
PV
/dev/sdc1
/dev/sdd1
/dev/sdb1
5.8.2. Object Selection
This section provides a series of tables that list the information you can display about the LVM objects
with the pvs, vgs, and lvs commands.
For convenience, a field name prefix can be dropped if it matches the default for the command. For
example, with the pvs command, name means pv_name, but with the vgs command, name is
interpreted as vg_name.
Executing the following command is the equivalent of executing pvs -o pv_free.
# pvs -o free
PFree
17.14G
17.09G
17.14G
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NOTE
The number of characters in the attribute fields in pvs, vgs, and lvs output may
increase in later releases. The existing character fields will not change position, but new
fields may be added to the end. You should take this into account when writing scripts
that search for particular attribute characters, searching for the character based on its
relative position to the beginning of the field, but not for its relative position to the end of
the field. For example, to search for the character p in the ninth bit of the lv_attr field,
you could search for the string "^/........p/", but you should not search for the string "/*p$/".
The pvs Command
Table 5.2, “pvs Display Fields” lists the display arguments of the pvs command, along with the field
name as it appears in the header display and a description of the field.
Table 5.2. pvs Display Fields
90
Argument
Header
Description
dev_size
DevSize
The size of the underlying device on which the physical
volume was created
pe_start
1st PE
Offset to the start of the first physical extent in the underlying
device
pv_attr
Attr
Status of the physical volume: (a)llocatable or e(x)ported.
pv_fmt
Fmt
The metadata format of the physical volume (lvm2 or lvm1)
pv_free
PFree
The free space remaining on the physical volume
pv_name
PV
The physical volume name
pv_pe_alloc_count
Alloc
Number of used physical extents
pv_pe_count
PE
Number of physical extents
pvseg_size
SSize
The segment size of the physical volume
pvseg_start
Start
The starting physical extent of the physical volume segment
pv_size
PSize
The size of the physical volume
pv_tags
PV Tags
LVM tags attached to the physical volume
pv_used
Used
The amount of space currently used on the physical volume
pv_uuid
PV UUID
The UUID of the physical volume
CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
The pvs command displays the following fields by default: pv_name, vg_name, pv_fmt, pv_attr,
pv_size, pv_free. The display is sorted by pv_name.
# pvs
PV
/dev/sdb1
/dev/sdc1
/dev/sdd1
VG
new_vg
new_vg
new_vg
Fmt
lvm2
lvm2
lvm2
Attr
aaa-
PSize
17.14G
17.14G
17.14G
PFree
17.14G
17.09G
17.13G
Using the -v argument with the pvs command adds the following fields to the default display:
dev_size, pv_uuid.
# pvs -v
Scanning for physical volume names
PV
VG
Fmt Attr PSize PFree DevSize PV UUID
/dev/sdb1 new_vg lvm2 a17.14G 17.14G 17.14G onFF2w-1fLC-ughJ-D9eBM7iv-6XqA-dqGeXY
/dev/sdc1 new_vg lvm2 a17.14G 17.09G 17.14G Joqlch-yWSj-kuEn-IdwM01S9-XO8M-mcpsVe
/dev/sdd1 new_vg lvm2 a17.14G 17.13G 17.14G yvfvZK-Cf31-j75k-dECm0RZ3-0dGW-tUqkCS
You can use the --segments argument of the pvs command to display information about each
physical volume segment. A segment is a group of extents. A segment view can be useful if you want to
see whether your logical volume is fragmented.
The pvs --segments command displays the following fields by default: pv_name, vg_name, pv_fmt,
pv_attr, pv_size, pv_free, pvseg_start, pvseg_size. The display is sorted by pv_name and
pvseg_size within the physical volume.
# pvs --segments
PV
VG
/dev/hda2 VolGroup00
/dev/hda2 VolGroup00
/dev/hda2 VolGroup00
/dev/sda1 vg
/dev/sda1 vg
/dev/sda1 vg
/dev/sda1 vg
/dev/sda1 vg
/dev/sda1 vg
/dev/sda1 vg
/dev/sda1 vg
/dev/sdb1 vg
/dev/sdc1 vg
/dev/sdd1 vg
/dev/sde1 vg
/dev/sdf1 vg
/dev/sdg1 vg
Fmt
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
lvm2
Attr
aaaaaaaaaaaaaaaaa-
PSize
37.16G
37.16G
37.16G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
17.14G
PFree Start SSize
32.00M
0 1172
32.00M 1172
16
32.00M 1188
1
16.75G
0
26
16.75G
26
24
16.75G
50
26
16.75G
76
24
16.75G
100
26
16.75G
126
24
16.75G
150
22
16.75G
172 4217
17.14G
0 4389
17.14G
0 4389
17.14G
0 4389
17.14G
0 4389
17.14G
0 4389
17.14G
0 4389
You can use the pvs -a command to see devices detected by LVM that have not been initialized as
LVM physical volumes.
# pvs -a
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Logical Volume Manager Administration
PV
/dev/VolGroup00/LogVol01
/dev/new_vg/lvol0
/dev/ram
/dev/ram0
/dev/ram2
/dev/ram3
/dev/ram4
/dev/ram5
/dev/ram6
/dev/root
/dev/sda
/dev/sdb
/dev/sdb1
/dev/sdc
/dev/sdc1
/dev/sdd
/dev/sdd1
VG
Fmt
Attr
------------new_vg lvm2 a-new_vg lvm2 a-new_vg lvm2 a-
PSize
0
0
0
0
0
0
0
0
0
0
0
0
17.14G
0
17.14G
0
17.14G
PFree
0
0
0
0
0
0
0
0
0
0
0
0
17.14G
0
17.09G
0
17.14G
The vgs Command
Table 5.3, “vgs Display Fields” lists the display arguments of the vgs command, along with the field
name as it appears in the header display and a description of the field.
Table 5.3. vgs Display Fields
92
Argument
Header
Description
lv_count
#LV
The number of logical volumes the volume group contains
max_lv
MaxLV
The maximum number of logical volumes allowed in the
volume group (0 if unlimited)
max_pv
MaxPV
The maximum number of physical volumes allowed in the
volume group (0 if unlimited)
pv_count
#PV
The number of physical volumes that define the volume
group
snap_count
#SN
The number of snapshots the volume group contains
vg_attr
Attr
Status of the volume group: (w)riteable, (r)eadonly,
resi(z)eable, e(x)ported, (p)artial and (c)lustered.
vg_extent_count
#Ext
The number of physical extents in the volume group
vg_extent_size
Ext
The size of the physical extents in the volume group
vg_fmt
Fmt
The metadata format of the volume group ( lvm2 or lvm1)
vg_free
VFree
Size of the free space remaining in the volume group
CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
Argument
Header
Description
vg_free_count
Free
Number of free physical extents in the volume group
vg_name
VG
The volume group name
vg_seqno
Seq
Number representing the revision of the volume group
vg_size
VSize
The size of the volume group
vg_sysid
SYS ID
LVM1 System ID
vg_tags
VG Tags
LVM tags attached to the volume group
vg_uuid
VG UUID
The UUID of the volume group
The vgs command displays the following fields by default: vg_name, pv_count, lv_count,
snap_count, vg_attr, vg_size, vg_free. The display is sorted by vg_name.
# vgs
VG
#PV #LV #SN Attr
VSize VFree
new_vg
3
1
1 wz--n- 51.42G 51.36G
Using the -v argument with the vgs command adds the following fields to the default display:
vg_extent_size, vg_uuid.
# vgs -v
Finding all volume groups
Finding volume group "new_vg"
VG
Attr
Ext
#PV #LV #SN VSize VFree VG UUID
new_vg wz--n- 4.00M
3
1
1 51.42G 51.36G jxQJ0a-ZKk0-OpMO-0118nlwO-wwqd-fD5D32
The lvs Command
Table 5.4, “lvs Display Fields” lists the display arguments of the lvs command, along with the field name
as it appears in the header display and a description of the field.
Table 5.4. lvs Display Fields
Argument
chunksize
Header
Description
Chunk
Unit size in a snapshot volume
chunk_size
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Logical Volume Manager Administration
Argument
Header
Description
copy_percent
Copy%
The synchronization percentage of a mirrored logical volume;
also used when physical extents are being moved with the
pv_move command
devices
Devices
The underlying devices that make up the logical volume: the
physical volumes, logical volumes, and start physical extents
and logical extents
lv_attr
Attr
The status of the logical volume. The logical volume attribute
bits are as follows:
Bit 1: Volume type: (m)irrored, (M)irrored without initial sync,
(o)rigin, (O)rigin with merging snapshot, (r)aid, (R)aid without
initial sync, (s)napshot, merging (S)napshot, (p)vmove, (v)irtual,
mirror or raid (i)mage, mirror or raid (I)mage out-of-sync, mirror
(l)og device, under (c)onversion, thin (V)olume, (t)hin pool,
(T)hin pool data, raid or thin pool m(e)tadata or pool metadata
spare,
Bit 2: Permissions: (w)riteable, (r)ead-only, (R)ead-only
activation of non-read-only volume
Bit 3: Allocation policy: (a)nywhere, (c)ontiguous, (i)nherited,
c(l)ing, (n)ormal. This is capitalized if the volume is currently
locked against allocation changes, for example while executing
the pvmove command.
Bit 4: fixed (m)inor
Bit 5: State: (a)ctive, (s)uspended, (I)nvalid snapshot, invalid
(S)uspended snapshot, snapshot (m)erge failed, suspended
snapshot (M)erge failed, mapped (d)evice present without
tables, mapped device present with (i)nactive table
Bit 6: device (o)pen
Bit 7: Target type: (m)irror, (r)aid, (s)napshot, (t)hin, (u)nknown,
(v)irtual. This groups logical volumes related to the same kernel
target together. So, for example, mirror images, mirror logs as
well as mirrors themselves appear as (m) if they use the original
device-mapper mirror kernel driver, whereas the raid
equivalents using the md raid kernel driver all appear as (r).
Snapshots using the original device-mapper driver appear as
(s), whereas snapshots of thin volumes using the thin
provisioning driver appear as (t).
Bit 8: Newly-allocated data blocks are overwritten with blocks of
(z)eroes before use.
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
Argument
Header
Bit 9: Volume Health: (p)artial, (r)efresh needed, (m)ismatches
Description
exist, (w)ritemostly. (p)artial signifies that one or more of the
Physical Volumes this Logical Volume uses is missing from the
system. (r)efresh signifies that one or more of the Physical
Volumes this RAID Logical Volume uses had suffered a write
error. The write error could be due to a temporary failure of that
Physical Volume or an indication that it is failing. The device
should be refreshed or replaced. (m)ismatches signifies that the
RAID logical volume has portions of the array that are not
coherent. Inconsistencies are discovered by initiating a check
operation on a RAID logical volume. (The scrubbing operations,
check and repair , can be performed on a RAID Logical
Volume by means of the lvchange command.) (w)ritemostly
signifies the devices in a RAID 1 logical volume that have been
marked write-mostly.
Bit 10: s(k)ip activation: this volume is flagged to be skipped
during activation.
lv_kernel_major
KMaj
Actual major device number of the logical volume (-1 if
inactive)
lv_kernel_minor
KMIN
Actual minor device number of the logical volume (-1 if
inactive)
lv_major
Maj
The persistent major device number of the logical volume (-1
if not specified)
lv_minor
Min
The persistent minor device number of the logical volume (-1
if not specified)
lv_name
LV
The name of the logical volume
lv_size
LSize
The size of the logical volume
lv_tags
LV Tags
LVM tags attached to the logical volume
lv_uuid
LV UUID
The UUID of the logical volume.
mirror_log
Log
Device on which the mirror log resides
modules
Modules
Corresponding kernel device-mapper target necessary to use
this logical volume
move_pv
Move
Source physical volume of a temporary logical volume
created with the pvmove command
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Logical Volume Manager Administration
Argument
Header
Description
origin
Origin
The origin device of a snapshot volume
Region
The unit size of a mirrored logical volume
seg_count
#Seg
The number of segments in the logical volume
seg_size
SSize
The size of the segments in the logical volume
seg_start
Start
Offset of the segment in the logical volume
seg_tags
Seg Tags
LVM tags attached to the segments of the logical volume
segtype
Type
The segment type of a logical volume (for example: mirror,
striped, linear)
snap_percent
Snap%
Current percentage of a snapshot volume that is in use
stripes
#Str
Number of stripes or mirrors in a logical volume
Stripe
Unit size of the stripe in a striped logical volume
regionsize
region_size
stripesize
stripe_size
The lvs command displays the following fields by default: lv_name, vg_name, lv_attr, lv_size,
origin, snap_percent, move_pv, mirror_log, copy_percent, convert_lv. The default display
is sorted by vg_name and lv_name within the volume group.
# lvs
LV
VG
Attr
LSize Origin Snap% Move Log Copy%
lvol0
new_vg owi-a- 52.00M
newvgsnap1 new_vg swi-a- 8.00M lvol0
0.20
Convert
Using the -v argument with the lvs command adds the following fields to the default display:
seg_count, lv_major, lv_minor, lv_kernel_major, lv_kernel_minor, lv_uuid.
# lvs -v
Finding all logical volumes
LV
VG
#Seg Attr
LSize Maj Min KMaj KMin Origin Snap%
Move Copy% Log Convert LV UUID
lvol0
new_vg
1 owi-a- 52.00M -1 -1 253 3
LBy1Tz-sr23-OjsI-LT03-nHLC-y8XW-EhCl78
newvgsnap1 new_vg
1 swi-a- 8.00M -1 -1 253 5
lvol0
0.20
1ye1OU-1cIu-o79k-20h2-ZGF0-qCJm-CfbsIx
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
You can use the --segments argument of the lvs command to display information with default
columns that emphasize the segment information. When you use the segments argument, the seg
prefix is optional. The lvs --segments command displays the following fields by default: lv_name,
vg_name, lv_attr, stripes, segtype, seg_size. The default display is sorted by vg_name,
lv_name within the volume group, and seg_start within the logical volume. If the logical volumes were
fragmented, the output from this command would show that.
# lvs --segments
LV
VG
LogVol00 VolGroup00
LogVol01 VolGroup00
lv
vg
lv
vg
lv
vg
lv
vg
Attr
#Str Type
SSize
-wi-ao
1 linear 36.62G
-wi-ao
1 linear 512.00M
-wi-a1 linear 104.00M
-wi-a1 linear 104.00M
-wi-a1 linear 104.00M
-wi-a1 linear 88.00M
Using the -v argument with the lvs --segments command adds the following fields to the default
display: seg_start, stripesize, chunksize.
# lvs -v --segments
Finding all logical volumes
LV
VG
Attr
Start SSize #Str Type
Stripe Chunk
lvol0
new_vg owi-a0 52.00M
1 linear
0
0
newvgsnap1 new_vg swi-a0
8.00M
1 linear
0 8.00K
The following example shows the default output of the lvs command on a system with one logical
volume configured, followed by the default output of the lvs command with the segments argument
specified.
# lvs
LV
VG
Attr
LSize Origin Snap%
lvol0 new_vg -wi-a- 52.00M
# lvs --segments
LV
VG
Attr
#Str Type
SSize
lvol0 new_vg -wi-a1 linear 52.00M
Move Log Copy%
5.8.3. Sorting LVM Reports
Normally the entire output of the lvs, vgs, or pvs command has to be generated and stored internally
before it can be sorted and columns aligned correctly. You can specify the --unbuffered argument to
display unsorted output as soon as it is generated.
To specify an alternative ordered list of columns to sort on, use the -O argument of any of the reporting
commands. It is not necessary to include these fields within the output itself.
The following example shows the output of the pvs command that displays the physical volume name,
size, and free space.
# pvs -o pv_name,pv_size,pv_free
PV
PSize PFree
/dev/sdb1 17.14G 17.14G
/dev/sdc1 17.14G 17.09G
/dev/sdd1 17.14G 17.14G
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The following example shows the same output, sorted by the free space field.
# pvs -o pv_name,pv_size,pv_free -O pv_free
PV
PSize PFree
/dev/sdc1 17.14G 17.09G
/dev/sdd1 17.14G 17.14G
/dev/sdb1 17.14G 17.14G
The following example shows that you do not need to display the field on which you are sorting.
# pvs -o pv_name,pv_size -O pv_free
PV
PSize
/dev/sdc1 17.14G
/dev/sdd1 17.14G
/dev/sdb1 17.14G
To display a reverse sort, precede a field you specify after the -O argument with the - character.
# pvs -o pv_name,pv_size,pv_free -O -pv_free
PV
PSize PFree
/dev/sdd1 17.14G 17.14G
/dev/sdb1 17.14G 17.14G
/dev/sdc1 17.14G 17.09G
5.8.4. Specifying Units
To specify the unit for the LVM report display, use the --units argument of the report command. You
can specify (b)ytes, (k)ilobytes, (m)egabytes, (g)igabytes, (t)erabytes, (e)xabytes, (p)etabytes, and
(h)uman-readable. The default display is human-readable. You can override the default by setting the
units parameter in the global section of the lvm.conf file.
The following example specifies the output of the pvs command in megabytes rather than the default
gigabytes.
# pvs --units m
PV
VG
/dev/sda1
/dev/sdb1 new_vg
/dev/sdc1 new_vg
/dev/sdd1 new_vg
Fmt
lvm2
lvm2
lvm2
lvm2
Attr
-aaa-
PSize
17555.40M
17552.00M
17552.00M
17552.00M
PFree
17555.40M
17552.00M
17500.00M
17552.00M
By default, units are displayed in powers of 2 (multiples of 1024). You can specify that units be displayed
in multiples of 1000 by capitalizing the unit specification (B, K, M, G, T, H).
The following command displays the output as a multiple of 1024, the default behavior.
# pvs
PV
/dev/sdb1
/dev/sdc1
/dev/sdd1
VG
new_vg
new_vg
new_vg
Fmt
lvm2
lvm2
lvm2
Attr
aaa-
PSize
17.14G
17.14G
17.14G
PFree
17.14G
17.09G
17.14G
The following command displays the output as a multiple of 1000.
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CHAPTER 5. LVM ADMINISTRATION WITH CLI COMMANDS
#
pvs --units G
PV
VG
/dev/sdb1 new_vg
/dev/sdc1 new_vg
/dev/sdd1 new_vg
Fmt
lvm2
lvm2
lvm2
Attr
aaa-
PSize
18.40G
18.40G
18.40G
PFree
18.40G
18.35G
18.40G
You can also specify (s)ectors (defined as 512 bytes) or custom units.
The following example displays the output of the pvs command as a number of sectors.
# pvs --units s
PV
VG
/dev/sdb1 new_vg
/dev/sdc1 new_vg
/dev/sdd1 new_vg
Fmt
lvm2
lvm2
lvm2
Attr
aaa-
PSize
35946496S
35946496S
35946496S
PFree
35946496S
35840000S
35946496S
The following example displays the output of the pvs command in units of 4 MB.
# pvs --units 4m
PV
VG
/dev/sdb1 new_vg
/dev/sdc1 new_vg
/dev/sdd1 new_vg
Fmt
lvm2
lvm2
lvm2
Attr
aaa-
PSize
4388.00U
4388.00U
4388.00U
PFree
4388.00U
4375.00U
4388.00U
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CHAPTER 6. LVM CONFIGURATION EXAMPLES
This chapter provides some basic LVM configuration examples.
6.1. CREATING AN LVM LOGICAL VOLUME ON THREE DISKS
This example creates an LVM logical volume called new_logical_volume that consists of the disks at
/dev/sda1, /dev/sdb1, and /dev/sdc1.
6.1.1. Creating the Physical Volumes
To use disks in a volume group, you label them as LVM physical volumes.

WARNING
This command destroys any data on /dev/sda1, /dev/sdb1, and /dev/sdc1.
# pvcreate
Physical
Physical
Physical
/dev/sda1 /dev/sdb1 /dev/sdc1
volume "/dev/sda1" successfully created
volume "/dev/sdb1" successfully created
volume "/dev/sdc1" successfully created
6.1.2. Creating the Volume Group
The following command creates the volume group new_vol_group.
# vgcreate new_vol_group /dev/sda1 /dev/sdb1 /dev/sdc1
Volume group "new_vol_group" successfully created
You can use the vgs command to display the attributes of the new volume group.
# vgs
VG
#PV #LV #SN Attr
VSize VFree
new_vol_group
3
0
0 wz--n- 51.45G 51.45G
6.1.3. Creating the Logical Volume
The following command creates the logical volume new_logical_volume from the volume group
new_vol_group. This example creates a logical volume that uses 2GB of the volume group.
# lvcreate -L2G -n new_logical_volume new_vol_group
Logical volume "new_logical_volume" created
6.1.4. Creating the File System
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CHAPTER 6. LVM CONFIGURATION EXAMPLES
The following command creates a GFS2 file system on the logical volume.
# mkfs.gfs2 -plock_nolock -j 1 /dev/new_vol_group/new_logical_volume
This will destroy any data on /dev/new_vol_group/new_logical_volume.
Are you sure you want to proceed? [y/n] y
Device:
Blocksize:
Filesystem Size:
Journals:
Resource Groups:
Locking Protocol:
Lock Table:
/dev/new_vol_group/new_logical_volume
4096
491460
1
8
lock_nolock
Syncing...
All Done
The following commands mount the logical volume and report the file system disk space usage.
# mount /dev/new_vol_group/new_logical_volume /mnt
[root@tng3-1 ~]# df
Filesystem
1K-blocks
Used Available Use% Mounted on
/dev/new_vol_group/new_logical_volume
1965840
20
1965820
1% /mnt
6.2. CREATING A STRIPED LOGICAL VOLUME
This example creates an LVM striped logical volume called striped_logical_volume that stripes
data across the disks at /dev/sda1, /dev/sdb1, and /dev/sdc1.
6.2.1. Creating the Physical Volumes
Label the disks you will use in the volume groups as LVM physical volumes.

WARNING
This command destroys any data on /dev/sda1, /dev/sdb1, and /dev/sdc1.
# pvcreate
Physical
Physical
Physical
/dev/sda1 /dev/sdb1 /dev/sdc1
volume "/dev/sda1" successfully created
volume "/dev/sdb1" successfully created
volume "/dev/sdc1" successfully created
6.2.2. Creating the Volume Group
The following command creates the volume group volgroup01.
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Logical Volume Manager Administration
# vgcreate volgroup01 /dev/sda1 /dev/sdb1 /dev/sdc1
Volume group "volgroup01" successfully created
You can use the vgs command to display the attributes of the new volume group.
# vgs
VG
volgroup01
#PV #LV #SN Attr
VSize VFree
3
0
0 wz--n- 51.45G 51.45G
6.2.3. Creating the Logical Volume
The following command creates the striped logical volume striped_logical_volume from the
volume group volgroup01. This example creates a logical volume that is 2 gigabytes in size, with three
stripes and a stripe size of 4 kilobytes.
# lvcreate -i3 -I4 -L2G -nstriped_logical_volume volgroup01
Rounding size (512 extents) up to stripe boundary size (513 extents)
Logical volume "striped_logical_volume" created
6.2.4. Creating the File System
The following command creates a GFS2 file system on the logical volume.
# mkfs.gfs2 -plock_nolock -j 1 /dev/volgroup01/striped_logical_volume
This will destroy any data on /dev/volgroup01/striped_logical_volume.
Are you sure you want to proceed? [y/n] y
Device:
Blocksize:
Filesystem Size:
Journals:
Resource Groups:
Locking Protocol:
Lock Table:
/dev/volgroup01/striped_logical_volume
4096
492484
1
8
lock_nolock
Syncing...
All Done
The following commands mount the logical volume and report the file system disk space usage.
# mount /dev/volgroup01/striped_logical_volume /mnt
[root@tng3-1 ~]# df
Filesystem
1K-blocks
Used Available Use%
/dev/mapper/VolGroup00-LogVol00
13902624
1656776 11528232 13%
/dev/hda1
101086
10787
85080 12%
tmpfs
127880
0
127880
0%
/dev/volgroup01/striped_logical_volume
1969936
20
1969916
1%
6.3. SPLITTING A VOLUME GROUP
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/
/boot
/dev/shm
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CHAPTER 6. LVM CONFIGURATION EXAMPLES
In this example, an existing volume group consists of three physical volumes. If there is enough unused
space on the physical volumes, a new volume group can be created without adding new disks.
In the initial set up, the logical volume mylv is carved from the volume group myvol, which in turn
consists of the three physical volumes, /dev/sda1, /dev/sdb1, and /dev/sdc1.
After completing this procedure, the volume group myvg will consist of /dev/sda1 and /dev/sdb1. A
second volume group, yourvg, will consist of /dev/sdc1.
6.3.1. Determining Free Space
You can use the pvscan command to determine how much free space is currently available in the
volume group.
# pvscan
PV /dev/sda1 VG myvg
lvm2 [17.15 GB
PV /dev/sdb1 VG myvg
lvm2 [17.15 GB
PV /dev/sdc1 VG myvg
lvm2 [17.15 GB
Total: 3 [51.45 GB] / in use: 3 [51.45
/ 0
free]
/ 12.15 GB free]
/ 15.80 GB free]
GB] / in no VG: 0 [0
]
6.3.2. Moving the Data
You can move all the used physical extents in /dev/sdc1 to /dev/sdb1 with the pvmove command.
The pvmove command can take a long time to execute.
# pvmove /dev/sdc1 /dev/sdb1
/dev/sdc1: Moved: 14.7%
/dev/sdc1: Moved: 30.3%
/dev/sdc1: Moved: 45.7%
/dev/sdc1: Moved: 61.0%
/dev/sdc1: Moved: 76.6%
/dev/sdc1: Moved: 92.2%
/dev/sdc1: Moved: 100.0%
After moving the data, you can see that all of the space on /dev/sdc1 is free.
# pvscan
PV /dev/sda1
VG myvg
PV /dev/sdb1
VG myvg
PV /dev/sdc1
VG myvg
Total: 3 [51.45 GB] / in
lvm2
lvm2
lvm2
use:
[17.15 GB / 0
free]
[17.15 GB / 10.80 GB free]
[17.15 GB / 17.15 GB free]
3 [51.45 GB] / in no VG: 0 [0
]
6.3.3. Splitting the Volume Group
To create the new volume group yourvg, use the vgsplit command to split the volume group myvg.
Before you can split the volume group, the logical volume must be inactive. If the file system is mounted,
you must unmount the file system before deactivating the logical volume.
You can deactivate the logical volumes with the lvchange command or the vgchange command. The
following command deactivates the logical volume mylv and then splits the volume group yourvg from
the volume group myvg, moving the physical volume /dev/sdc1 into the new volume group yourvg.
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Logical Volume Manager Administration
# lvchange -a n /dev/myvg/mylv
# vgsplit myvg yourvg /dev/sdc1
Volume group "yourvg" successfully split from "myvg"
You can use the vgs command to see the attributes of the two volume groups.
# vgs
VG
#PV #LV #SN Attr
VSize VFree
myvg
2
1
0 wz--n- 34.30G 10.80G
yourvg
1
0
0 wz--n- 17.15G 17.15G
6.3.4. Creating the New Logical Volume
After creating the new volume group, you can create the new logical volume yourlv.
# lvcreate -L5G -n yourlv yourvg
Logical volume "yourlv" created
6.3.5. Making a File System and Mounting the New Logical Volume
You can make a file system on the new logical volume and mount it.
# mkfs.gfs2 -plock_nolock -j 1 /dev/yourvg/yourlv
This will destroy any data on /dev/yourvg/yourlv.
Are you sure you want to proceed? [y/n] y
Device:
Blocksize:
Filesystem Size:
Journals:
Resource Groups:
Locking Protocol:
Lock Table:
/dev/yourvg/yourlv
4096
1277816
1
20
lock_nolock
Syncing...
All Done
[root@tng3-1 ~]# mount /dev/yourvg/yourlv /mnt
6.3.6. Activating and Mounting the Original Logical Volume
Since you had to deactivate the logical volume mylv, you need to activate it again before you can mount
it.
# lvchange -a y /dev/myvg/mylv
[root@tng3-1 ~]# mount /dev/myvg/mylv /mnt
[root@tng3-1 ~]# df
Filesystem
1K-blocks
Used Available Use% Mounted on
/dev/yourvg/yourlv
24507776
32 24507744
1% /mnt
/dev/myvg/mylv
24507776
32 24507744
1% /mnt
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CHAPTER 6. LVM CONFIGURATION EXAMPLES
6.4. REMOVING A DISK FROM A LOGICAL VOLUME
This example shows how you can remove a disk from an existing logical volume, either to replace the
disk or to use the disk as part of a different volume. In order to remove a disk, you must first move the
extents on the LVM physical volume to a different disk or set of disks.
6.4.1. Moving Extents to Existing Physical Volumes
In this example, the logical volume is distributed across four physical volumes in the volume group myvg.
# pvs -o+pv_used
PV
VG
/dev/sda1 myvg
/dev/sdb1 myvg
/dev/sdc1 myvg
/dev/sdd1 myvg
Fmt
lvm2
lvm2
lvm2
lvm2
Attr
aaaa-
PSize
17.15G
17.15G
17.15G
17.15G
PFree Used
12.15G 5.00G
12.15G 5.00G
12.15G 5.00G
2.15G 15.00G
We want to move the extents off of /dev/sdb1 so that we can remove it from the volume group.
If there are enough free extents on the other physical volumes in the volume group, you can execute the
pvmove command on the device you want to remove with no other options and the extents will be
distributed to the other devices.
# pvmove /dev/sdb1
/dev/sdb1: Moved: 2.0%
...
/dev/sdb1: Moved: 79.2%
...
/dev/sdb1: Moved: 100.0%
After the pvmove command has finished executing, the distribution of extents is as follows:
# pvs -o+pv_used
PV
VG
/dev/sda1 myvg
/dev/sdb1 myvg
/dev/sdc1 myvg
/dev/sdd1 myvg
Fmt
lvm2
lvm2
lvm2
lvm2
Attr
aaaa-
PSize PFree Used
17.15G 7.15G 10.00G
17.15G 17.15G
0
17.15G 12.15G 5.00G
17.15G 2.15G 15.00G
Use the vgreduce command to remove the physical volume /dev/sdb1 from the volume group.
# vgreduce myvg /dev/sdb1
Removed "/dev/sdb1" from volume group "myvg"
[root@tng3-1 ~]# pvs
PV
VG
Fmt Attr PSize PFree
/dev/sda1 myvg lvm2 a17.15G 7.15G
/dev/sdb1
lvm2 -17.15G 17.15G
/dev/sdc1 myvg lvm2 a17.15G 12.15G
/dev/sdd1 myvg lvm2 a17.15G 2.15G
The disk can now be physically removed or allocated to other users.
6.4.2. Moving Extents to a New Disk
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Logical Volume Manager Administration
In this example, the logical volume is distributed across three physical volumes in the volume group
myvg as follows:
# pvs -o+pv_used
PV
VG
/dev/sda1 myvg
/dev/sdb1 myvg
/dev/sdc1 myvg
Fmt
lvm2
lvm2
lvm2
Attr
aaa-
PSize PFree Used
17.15G 7.15G 10.00G
17.15G 15.15G 2.00G
17.15G 15.15G 2.00G
We want to move the extents of /dev/sdb1 to a new device, /dev/sdd1.
6.4.2.1. Creating the New Physical Volume
Create a new physical volume from /dev/sdd1.
# pvcreate /dev/sdd1
Physical volume "/dev/sdd1" successfully created
6.4.2.2. Adding the New Physical Volume to the Volume Group
Add /dev/sdd1 to the existing volume group myvg.
# vgextend myvg /dev/sdd1
Volume group "myvg" successfully extended
[root@tng3-1]# pvs -o+pv_used
PV
VG
Fmt Attr PSize PFree Used
/dev/sda1
myvg lvm2 a17.15G 7.15G 10.00G
/dev/sdb1
myvg lvm2 a17.15G 15.15G 2.00G
/dev/sdc1
myvg lvm2 a17.15G 15.15G 2.00G
/dev/sdd1
myvg lvm2 a17.15G 17.15G
0
6.4.2.3. Moving the Data
Use the pvmove command to move the data from /dev/sdb1 to /dev/sdd1.
# pvmove /dev/sdb1 /dev/sdd1
/dev/sdb1: Moved: 10.0%
...
/dev/sdb1: Moved: 79.7%
...
/dev/sdb1: Moved: 100.0%
[root@tng3-1]# pvs
PV
VG
/dev/sda1
myvg
/dev/sdb1
myvg
/dev/sdc1
myvg
/dev/sdd1
myvg
-o+pv_used
Fmt Attr PSize
lvm2 a17.15G
lvm2 a17.15G
lvm2 a17.15G
lvm2 a17.15G
PFree Used
7.15G 10.00G
17.15G
0
15.15G 2.00G
15.15G 2.00G
6.4.2.4. Removing the Old Physical Volume from the Volume Group
After you have moved the data off /dev/sdb1, you can remove it from the volume group.
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CHAPTER 6. LVM CONFIGURATION EXAMPLES
# vgreduce myvg /dev/sdb1
Removed "/dev/sdb1" from volume group "myvg"
You can now reallocate the disk to another volume group or remove the disk from the system.
6.5. CREATING A MIRRORED LVM LOGICAL VOLUME IN A CLUSTER
Creating a mirrored LVM logical volume in a cluster requires the same commands and procedures as
creating a mirrored LVM logical volume on a single node. However, in order to create a mirrored LVM
volume in a cluster the cluster and cluster mirror infrastructure must be running, the cluster must be
quorate, and the locking type in the lvm.conf file must be set correctly to enable cluster locking, either
directly or by means of the lvmconf command as described in Section 4.1, “Creating LVM Volumes in a
Cluster”.
The following procedure creates a mirrored LVM volume in a cluster. First the procedure checks to see
whether the cluster services are installed and running, then the procedure creates the mirrored volume.
1. In order to create a mirrored logical volume that is shared by all of the nodes in a cluster, the
locking type must be set correctly in the lvm.conf file in every node of the cluster. By default,
the locking type is set to local. To change this, execute the following command in each node of
the cluster to enable clustered locking:
# /sbin/lvmconf --enable-cluster
NOTE
As of Red Hat Enterprise Linux 6.7, the lvmconf command provides a -services option that will also enable the services required for LVM in a cluster,
a --mirrorservice option that enables the cmirrord service, and a -startstopservices option that immediately starts or stops the services that
have been enabled. For information on the lvmconf command, see the lvmconf
man page.
2. To create a clustered logical volume, the cluster infrastructure must be up and running on every
node in the cluster. The following example verifies that the clvmd daemon is running on the
node from which it was issued:
ps auxw | grep clvmd
root
17642 0.0 0.1 32164 1072 ?
clvmd -T20 -t 90
Ssl
Apr06
0:00
The following command shows the local view of the cluster status:
# cman_tool services
fence domain
member count 3
victim count 0
victim now
0
master nodeid 2
wait state
none
members
1 2 3
107
Logical Volume Manager Administration
dlm lockspaces
name
clvmd
id
0x4104eefa
flags
0x00000000
change
member 3 joined 1 remove 0 failed 0 seq 1,1
members
1 2 3
3. Ensure that the cmirror package is installed.
4. Start the cmirrord service.
# service cmirrord start
Starting cmirrord:
]
[
OK
5. Create the mirror. The first step is creating the physical volumes. The following commands
create three physical volumes. Two of the physical volumes will be used for the legs of the
mirror, and the third physical volume will contain the mirror log.
# pvcreate /dev/sdb1
Physical volume "/dev/sdb1" successfully created
[root@doc-07 ~]# pvcreate /dev/sdc1
Physical volume "/dev/sdc1" successfully created
[root@doc-07 ~]# pvcreate /dev/sdd1
Physical volume "/dev/sdd1" successfully created
6. Create the volume group. This example creates a volume group vg001 that consists of the three
physical volumes that were created in the previous step.
# vgcreate vg001 /dev/sdb1 /dev/sdc1 /dev/sdd1
Clustered volume group "vg001" successfully created
Note that the output of the vgcreate command indicates that the volume group is clustered.
You can verify that a volume group is clustered with the vgs command, which will show the
volume group's attributes. If a volume group is clustered, it will show a c attribute.
vgs vg001
VG
#PV #LV #SN Attr
VSize VFree
vg001
3
0
0 wz--nc 68.97G 68.97G
7. Create the mirrored logical volume. This example creates the logical volume mirrorlv from the
volume group vg001. This volume has one mirror leg. This example specifies which extents of
the physical volume will be used for the logical volume.
# lvcreate -l 1000 -m1 vg001 -n mirrorlv /dev/sdb1:1-1000
/dev/sdc1:1-1000 /dev/sdd1:0
Logical volume "mirrorlv" created
You can use the lvs command to display the progress of the mirror creation. The following
example shows that the mirror is 47% synced, then 91% synced, then 100% synced when the
mirror is complete.
# lvs vg001/mirrorlv
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CHAPTER 6. LVM CONFIGURATION EXAMPLES
LV
VG
Attr
LSize Origin Snap%
Copy% Convert
mirrorlv vg001
mwi-a- 3.91G
47.00
[root@doc-07 log]# lvs vg001/mirrorlv
LV
VG
Attr
LSize Origin Snap%
Copy% Convert
mirrorlv vg001
mwi-a- 3.91G
91.00
[root@doc-07 ~]# lvs vg001/mirrorlv
LV
VG
Attr
LSize Origin Snap%
Copy% Convert
mirrorlv vg001
mwi-a- 3.91G
100.00
Move Log
vg001_mlog
Move Log
vg001_mlog
Move Log
vg001_mlog
The completion of the mirror is noted in the system log:
May 10 14:52:52 doc-07 [19402]: Monitoring mirror device vg001mirrorlv for events
May 10 14:55:00 doc-07 lvm[19402]: vg001-mirrorlv is now in-sync
8. You can use the lvs with the -o +devices options to display the configuration of the mirror,
including which devices make up the mirror legs. You can see that the logical volume in this
example is composed of two linear images and one log.
# lvs -a -o +devices
LV
VG
Attr
LSize Origin Snap%
Log
Copy% Convert Devices
mirrorlv
vg001
mwi-a- 3.91G
mirrorlv_mlog 100.00
mirrorlv_mimage_0(0),mirrorlv_mimage_1(0)
[mirrorlv_mimage_0] vg001
iwi-ao 3.91G
/dev/sdb1(1)
[mirrorlv_mimage_1] vg001
iwi-ao 3.91G
/dev/sdc1(1)
[mirrorlv_mlog]
vg001
lwi-ao 4.00M
/dev/sdd1(0)
Move
You can use the seg_pe_ranges option of the lvs to display the data layout. You can use this
option to verify that your layout is properly redundant. The output of this command displays PE
ranges in the same format that the lvcreate and lvresize commands take as input.
# lvs -a -o +seg_pe_ranges --segments
PE Ranges
mirrorlv_mimage_0:0-999 mirrorlv_mimage_1:0-999
/dev/sdb1:1-1000
/dev/sdc1:1-1000
/dev/sdd1:0-0
NOTE
For information on recovering from the failure of one of the legs of an LVM mirrored
volume, see Section 7.3, “Recovering from LVM Mirror Failure”.
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Logical Volume Manager Administration
CHAPTER 7. LVM TROUBLESHOOTING
This chapter provide instructions for troubleshooting a variety of LVM issues.
7.1. TROUBLESHOOTING DIAGNOSTICS
If a command is not working as expected, you can gather diagnostics in the following ways:
Use the -v, -vv, -vvv, or -vvvv argument of any command for increasingly verbose levels of
output.
If the problem is related to the logical volume activation, set 'activation = 1' in the 'log' section of
the configuration file and run the command with the -vvvv argument. After you have finished
examining this output be sure to reset this parameter to 0, to avoid possible problems with the
machine locking during low memory situations.
Run the lvmdump command, which provides an information dump for diagnostic purposes. For
information, see the lvmdump(8) man page.
Execute the lvs -v, pvs -a or dmsetup info -c command for additional system
information.
Examine the last backup of the metadata in the /etc/lvm/backup file and archived versions in
the /etc/lvm/archive file.
Check the current configuration information by running the lvmconfig command.
Check the .cache file in the /etc/lvm directory for a record of which devices have physical
volumes on them.
7.2. DISPLAYING INFORMATION ON FAILED DEVICES
You can use the -P argument of the lvs or vgs command to display information about a failed volume
that would otherwise not appear in the output. This argument permits some operations even though the
metadata is not completely consistent internally. For example, if one of the devices that made up the
volume group vg failed, the vgs command might show the following output.
# vgs -o +devices
Volume group "vg" not found
If you specify the -P argument of the vgs command, the volume group is still unusable but you can see
more information about the failed device.
# vgs -P -o +devices
Partial mode. Incomplete volume groups will be activated read-only.
VG
#PV #LV #SN Attr
VSize VFree Devices
vg
9
2
0 rz-pn- 2.11T 2.07T unknown device(0)
vg
9
2
0 rz-pn- 2.11T 2.07T unknown device(5120),/dev/sda1(0)
In this example, the failed device caused both a linear and a striped logical volume in the volume group to
fail. The lvs command without the -P argument shows the following output.
110
CHAPTER 7. LVM TROUBLESHOOTING
# lvs -a -o +devices
Volume group "vg" not found
Using the -P argument shows the logical volumes that have failed.
# lvs -P -a -o +devices
Partial mode. Incomplete volume groups will be activated read-only.
LV
VG
Attr
LSize Origin Snap% Move Log Copy% Devices
linear vg
-wi-a- 20.00G
unknown
device(0)
stripe vg
-wi-a- 20.00G
unknown
device(5120),/dev/sda1(0)
The following examples show the output of the pvs and lvs commands with the -P argument specified
when a leg of a mirrored logical volume has failed.
#
vgs -a -o +devices -P
Partial mode. Incomplete volume groups will be activated read-only.
VG
#PV #LV #SN Attr
VSize VFree Devices
corey
4
4
0 rz-pnc 1.58T 1.34T
my_mirror_mimage_0(0),my_mirror_mimage_1(0)
corey
4
4
0 rz-pnc 1.58T 1.34T /dev/sdd1(0)
corey
4
4
0 rz-pnc 1.58T 1.34T unknown device(0)
corey
4
4
0 rz-pnc 1.58T 1.34T /dev/sdb1(0)
# lvs -a -o +devices -P
Partial mode. Incomplete volume groups will be activated read-only.
LV
VG
Attr
LSize
Origin Snap% Move Log
Copy% Devices
my_mirror
corey mwi-a- 120.00G
my_mirror_mlog
1.95 my_mirror_mimage_0(0),my_mirror_mimage_1(0)
[my_mirror_mimage_0] corey iwi-ao 120.00G
unknown device(0)
[my_mirror_mimage_1] corey iwi-ao 120.00G
/dev/sdb1(0)
[my_mirror_mlog]
corey lwi-ao
4.00M
/dev/sdd1(0)
7.3. RECOVERING FROM LVM MIRROR FAILURE
This section provides an example of recovering from a situation where one leg of an LVM mirrored
volume fails because the underlying device for a physical volume goes down and the
mirror_log_fault_policy parameter is set to remove, requiring that you manually rebuild the
mirror. For information on setting the mirror_log_fault_policy parameter, see Section 5.4.3.1,
“Mirrored Logical Volume Failure Policy”.
When a mirror leg fails, LVM converts the mirrored volume into a linear volume, which continues to
operate as before but without the mirrored redundancy. At that point, you can add a new disk device to
the system to use as a replacement physical device and rebuild the mirror.
The following command creates the physical volumes which will be used for the mirror.
# pvcreate /dev/sd[abcdefgh][12]
111
Logical Volume Manager Administration
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
Physical
volume
volume
volume
volume
volume
volume
volume
volume
volume
volume
volume
volume
volume
volume
volume
volume
"/dev/sda1"
"/dev/sda2"
"/dev/sdb1"
"/dev/sdb2"
"/dev/sdc1"
"/dev/sdc2"
"/dev/sdd1"
"/dev/sdd2"
"/dev/sde1"
"/dev/sde2"
"/dev/sdf1"
"/dev/sdf2"
"/dev/sdg1"
"/dev/sdg2"
"/dev/sdh1"
"/dev/sdh2"
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
successfully
created
created
created
created
created
created
created
created
created
created
created
created
created
created
created
created
The following commands creates the volume group vg and the mirrored volume groupfs.
# vgcreate vg /dev/sd[abcdefgh][12]
Volume group "vg" successfully created
[root@link-08 ~]# lvcreate -L 750M -n groupfs -m 1 vg /dev/sda1 /dev/sdb1
/dev/sdc1
Rounding up size to full physical extent 752.00 MB
Logical volume "groupfs" created
You can use the lvs command to verify the layout of the mirrored volume and the underlying devices for
the mirror leg and the mirror log. Note that in the first example the mirror is not yet completely synced;
you should wait until the Copy% field displays 100.00 before continuing.
# lvs -a -o +devices
LV
VG
Attr
LSize
Origin Snap%
Copy% Devices
groupfs
vg
mwi-a- 752.00M
21.28 groupfs_mimage_0(0),groupfs_mimage_1(0)
[groupfs_mimage_0] vg
iwi-ao 752.00M
/dev/sda1(0)
[groupfs_mimage_1] vg
iwi-ao 752.00M
/dev/sdb1(0)
[groupfs_mlog]
vg
lwi-ao
4.00M
/dev/sdc1(0)
[root@link-08 ~]# lvs -a -o +devices
LV
VG
Attr
LSize
Origin Snap%
Copy% Devices
groupfs
vg
mwi-a- 752.00M
100.00 groupfs_mimage_0(0),groupfs_mimage_1(0)
[groupfs_mimage_0] vg
iwi-ao 752.00M
/dev/sda1(0)
[groupfs_mimage_1] vg
iwi-ao 752.00M
/dev/sdb1(0)
[groupfs_mlog]
vg
lwi-ao
4.00M
i
/dev/sdc1(0)
112
Move Log
groupfs_mlog
Move Log
groupfs_mlog
CHAPTER 7. LVM TROUBLESHOOTING
In this example, the primary leg of the mirror /dev/sda1 fails. Any write activity to the mirrored volume
causes LVM to detect the failed mirror. When this occurs, LVM converts the mirror into a single linear
volume. In this case, to trigger the conversion, we execute a dd command
# dd if=/dev/zero of=/dev/vg/groupfs count=10
10+0 records in
10+0 records out
You can use the lvs command to verify that the device is now a linear device. Because of the failed
disk, I/O errors occur.
# lvs -a -o +devices
/dev/sda1: read failed after 0 of 2048 at 0: Input/output error
/dev/sda2: read failed after 0 of 2048 at 0: Input/output error
LV
VG
Attr
LSize
Origin Snap% Move Log Copy% Devices
groupfs vg
-wi-a- 752.00M
/dev/sdb1(0)
At this point you should still be able to use the logical volume, but there will be no mirror redundancy.
To rebuild the mirrored volume, you replace the broken drive and recreate the physical volume. If you
use the same disk rather than replacing it with a new one, you will see "inconsistent" warnings when you
run the pvcreate command. You can prevent that warning from appearing by executing the vgreduce
--removemissing command.
# pvcreate /dev/sdi[12]
Physical volume "/dev/sdi1" successfully created
Physical volume "/dev/sdi2" successfully created
[root@link-08 ~]# pvscan
PV /dev/sdb1
VG vg
lvm2 [67.83 GB / 67.10 GB free]
PV /dev/sdb2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdc1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdc2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdd1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdd2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sde1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sde2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdf1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdf2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdg1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdg2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdh1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdh2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdi1
lvm2 [603.94 GB]
PV /dev/sdi2
lvm2 [603.94 GB]
Total: 16 [2.11 TB] / in use: 14 [949.65 GB] / in no VG: 2 [1.18 TB]
Next you extend the original volume group with the new physical volume.
# vgextend vg /dev/sdi[12]
Volume group "vg" successfully extended
# pvscan
PV /dev/sdb1
VG vg
lvm2 [67.83 GB / 67.10 GB free]
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Logical Volume Manager Administration
PV /dev/sdb2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdc1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdc2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdd1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdd2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sde1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sde2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdf1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdf2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdg1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdg2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdh1
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdh2
VG vg
lvm2 [67.83 GB / 67.83 GB free]
PV /dev/sdi1
VG vg
lvm2 [603.93 GB / 603.93 GB free]
PV /dev/sdi2
VG vg
lvm2 [603.93 GB / 603.93 GB free]
Total: 16 [2.11 TB] / in use: 16 [2.11 TB] / in no VG: 0 [0
]
Convert the linear volume back to its original mirrored state.
# lvconvert -m 1 /dev/vg/groupfs /dev/sdi1 /dev/sdb1 /dev/sdc1
Logical volume mirror converted.
You can use the lvs command to verify that the mirror is restored.
# lvs -a -o +devices
LV
VG
Attr
LSize
Origin Snap%
Copy% Devices
groupfs
vg
mwi-a- 752.00M
68.62 groupfs_mimage_0(0),groupfs_mimage_1(0)
[groupfs_mimage_0] vg
iwi-ao 752.00M
/dev/sdb1(0)
[groupfs_mimage_1] vg
iwi-ao 752.00M
/dev/sdi1(0)
[groupfs_mlog]
vg
lwi-ao
4.00M
/dev/sdc1(0)
Move Log
groupfs_mlog
7.4. RECOVERING PHYSICAL VOLUME METADATA
If the volume group metadata area of a physical volume is accidentally overwritten or otherwise
destroyed, you will get an error message indicating that the metadata area is incorrect, or that the system
was unable to find a physical volume with a particular UUID. You may be able to recover the data the
physical volume by writing a new metadata area on the physical volume specifying the same UUID as
the lost metadata.

114
WARNING
You should not attempt this procedure with a working LVM logical volume. You will
lose your data if you specify the incorrect UUID.
CHAPTER 7. LVM TROUBLESHOOTING
The following example shows the sort of output you may see if the metadata area is missing or
corrupted.
# lvs -a -o +devices
Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
Couldn't find all physical volumes for volume group VG.
Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
Couldn't find all physical volumes for volume group VG.
...
You may be able to find the UUID for the physical volume that was overwritten by looking in the
/etc/lvm/archive directory. Look in the file VolumeGroupName_xxxx.vg for the last known valid
archived LVM metadata for that volume group.
Alternately, you may find that deactivating the volume and setting the partial (-P) argument will
enable you to find the UUID of the missing corrupted physical volume.
# vgchange -an --partial
Partial mode. Incomplete volume groups will be activated read-only.
Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
Couldn't find device with uuid 'FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk'.
...
Use the --uuid and --restorefile arguments of the pvcreate command to restore the physical
volume. The following example labels the /dev/sdh1 device as a physical volume with the UUID
indicated above, FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk. This command restores the
physical volume label with the metadata information contained in VG_00050.vg, the most recent good
archived metadata for the volume group. The restorefile argument instructs the pvcreate
command to make the new physical volume compatible with the old one on the volume group, ensuring
that the new metadata will not be placed where the old physical volume contained data (which could
happen, for example, if the original pvcreate command had used the command line arguments that
control metadata placement, or if the physical volume was originally created using a different version of
the software that used different defaults). The pvcreate command overwrites only the LVM metadata
areas and does not affect the existing data areas.
# pvcreate --uuid "FmGRh3-zhok-iVI8-7qTD-S5BI-MAEN-NYM5Sk" --restorefile
/etc/lvm/archive/VG_00050.vg /dev/sdh1
Physical volume "/dev/sdh1" successfully created
You can then use the vgcfgrestore command to restore the volume group's metadata.
# vgcfgrestore VG
Restored volume group VG
You can now display the logical volumes.
# lvs -a -o +devices
LV
VG
Attr
LSize
Origin Snap%
stripe VG
-wi--- 300.00G
(0),/dev/sda1(0)
stripe VG
-wi--- 300.00G
(34728),/dev/sdb1(0)
Move Log Copy%
Devices
/dev/sdh1
/dev/sdh1
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The following commands activate the volumes and display the active volumes.
# lvchange -ay /dev/VG/stripe
[root@link-07 backup]# lvs -a -o +devices
LV
VG
Attr
LSize
Origin Snap%
stripe VG
-wi-a- 300.00G
(0),/dev/sda1(0)
stripe VG
-wi-a- 300.00G
(34728),/dev/sdb1(0)
Move Log Copy%
Devices
/dev/sdh1
/dev/sdh1
If the on-disk LVM metadata takes as least as much space as what overrode it, this command can
recover the physical volume. If what overrode the metadata went past the metadata area, the data on the
volume may have been affected. You might be able to use the fsck command to recover that data.
7.5. REPLACING A MISSING PHYSICAL VOLUME
If a physical volume fails or otherwise needs to be replaced, you can label a new physical volume to
replace the one that has been lost in the existing volume group by following the same procedure as you
would for recovering physical volume metadata, described in Section 7.4, “Recovering Physical Volume
Metadata”. You can use the --partial and --verbose arguments of the vgdisplay command to
display the UUIDs and sizes of any physical volumes that are no longer present. If you wish to substitute
another physical volume of the same size, you can use the pvcreate command with the -restorefile and --uuid arguments to initialize a new device with the same UUID as the missing
physical volume. You can then use the vgcfgrestore command to restore the volume group's
metadata.
7.6. REMOVING LOST PHYSICAL VOLUMES FROM A VOLUME GROUP
If you lose a physical volume, you can activate the remaining physical volumes in the volume group with
the --partial argument of the vgchange command. You can remove all the logical volumes that used
that physical volume from the volume group with the --removemissing argument of the vgreduce
command.
It is recommended that you run the vgreduce command with the --test argument to verify what you
will be destroying.
Like most LVM operations, the vgreduce command is reversible in a sense if you immediately use the
vgcfgrestore command to restore the volume group metadata to its previous state. For example, if
you used the --removemissing argument of the vgreduce command without the --test argument
and find you have removed logical volumes you wanted to keep, you can still replace the physical
volume and use another vgcfgrestore command to return the volume group to its previous state.
7.7. INSUFFICIENT FREE EXTENTS FOR A LOGICAL VOLUME
You may get the error message "Insufficient free extents" when creating a logical volume when you think
you have enough extents based on the output of the vgdisplay or vgs commands. This is because
these commands round figures to 2 decimal places to provide human-readable output. To specify exact
size, use free physical extent count instead of some multiple of bytes to determine the size of the logical
volume.
The vgdisplay command, by default, includes this line of output that indicates the free physical extents.
# vgdisplay
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--- Volume group --...
Free PE / Size
8780 / 34.30 GB
Alternately, you can use the vg_free_count and vg_extent_count arguments of the vgs command
to display the free extents and the total number of extents.
# vgs -o +vg_free_count,vg_extent_count
VG
#PV #LV #SN Attr
VSize VFree Free #Ext
testvg
2
0
0 wz--n- 34.30G 34.30G 8780 8780
With 8780 free physical extents, you can enter the following command, using the lower-case l argument
to use extents instead of bytes:
# lvcreate -l8780 -n testlv testvg
This uses all the free extents in the volume group.
# vgs -o +vg_free_count,vg_extent_count
VG
#PV #LV #SN Attr
VSize VFree Free #Ext
testvg
2
1
0 wz--n- 34.30G
0
0 8780
Alternately, you can extend the logical volume to use a percentage of the remaining free space in the
volume group by using the -l argument of the lvcreate command. For information, see Section 5.4.1,
“Creating Linear Logical Volumes”.
7.8. DUPLICATE PV WARNINGS FOR MULTIPATHED DEVICES
When using LVM with multipathed storage, some LVM commands (such as vgs or lvchange) may
display messages such as the following when listing a volume group or logical volume.
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/dm-5 not
/dev/sdd
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/emcpowerb
not /dev/sde
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using /dev/sddlmab
not /dev/sdf
After providing information on the root cause for these warnings, this section describes how to address
this issue in the following two cases.
The two devices displayed in the output are both single paths to the same device
The two devices displayed in the output are both multipath maps
7.8.1. Root Cause of Duplicate PV Warning
With a default configuration, LVM commands will scan for devices in /dev and check every resulting
device for LVM metadata. This is caused by the default filter in the /etc/lvm/lvm.conf, which is as
follows:
filter = [ "a/.*/" ]
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When using Device Mapper Multipath or other multipath software such as EMC PowerPath or Hitachi
Dynamic Link Manager (HDLM), each path to a particular logical unit number (LUN) is registered as a
different SCSI device, such as /dev/sdb or /dev/sdc. The multipath software will then create a new
device that maps to those individual paths, such as /dev/mapper/mpath1 or /dev/mapper/mpatha
for Device Mapper Multipath, /dev/emcpowera for EMC PowerPath, or /dev/sddlmab for Hitachi
HDLM. Since each LUN has multiple device nodes in /dev that point to the same underlying data, they
all contain the same LVM metadata and thus LVM commands will find the same metadata multiple times
and report them as duplicates.
These duplicate messages are only warnings and do not mean the LVM operation has failed. Rather,
they are alerting the user that only one of the devices has been used as a physical volume and the others
are being ignored. If the messages indicate the incorrect device is being chosen or if the warnings are
disruptive to users, then a filter can be applied to search only the necessary devices for physical
volumes, and to leave out any underlying paths to multipath devices.
7.8.2. Duplicate Warnings for Single Paths
The following example shows a duplicate PV warning in which the duplicate devices displayed are both
single paths to the same device. In this case, both /dev/sdd and /dev/sdf can be found under the
same multipath map in the output to the multipath -ll command.
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using **/dev/sdd**
not **/dev/sdf**
To prevent this warning from appearing, you can configure a filter in the /etc/lvm/lvm.conf file to
restrict the devices that LVM will search for metadata. The filter is a list of patterns that will be applied to
each device found by a scan of /dev (or the directory specified by the dir keyword in the
/etc/lvm/lvm.conf file). Patterns are regular expressions delimited by any character and preceded
by a (for accept) or r (for reject). The list is traversed in order, and the first regex that matches a device
determines if the device will be accepted or rejected (ignored). Devices that don’t match any patterns are
accepted. For general information on LVM filters, see Section 5.5, “Controlling LVM Device Scans with
Filters”.
The filter you configure should include all devices that need to be checked for LVM metadata, such as
the local hard drive with the root volume group on it and any multipathed devices. By rejecting the
underlying paths to a multipath device (such as /dev/sdb, /dev/sdd, and so on) you can avoid these
duplicate PV warnings, since each unique metadata area will only be found once on the multipath device
itself.
The following examples show filters that will avoid duplicate PV warnings due to multiple storage paths
being available.
This filter accepts the second partition on the first hard drive (/dev/sda and any devicemapper-multipath devices, while rejecting everything else.
filter = [ "a|/dev/sda2$|", "a|/dev/mapper/mpath.*|", "r|.*|" ]
This filter accepts all HP SmartArray controllers and any EMC PowerPath devices.
filter = [ "a|/dev/cciss/.*|", "a|/dev/emcpower.*|", "r|.*|" ]
This filter accepts any partitions on the first IDE drive and any multipath devices.
filter = [ "a|/dev/hda.*|", "a|/dev/mapper/mpath.*|", "r|.*|" ]
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NOTE
When adding a new filter to the /etc/lvm/lvm.conf file, ensure that the original filter is
either commented out with a # or is removed.
Once a filter has been configured and the /etc/lvm/lvm.conf file has been saved, check the output
of these commands to ensure that no physical volumes or volume groups are missing.
# pvscan
# vgscan
You can also test a filter on the fly, without modifying the /etc/lvm/lvm.conf file, by adding the -config argument to the LVM command, as in the following example.
# lvs --config 'devices{ filter = [ "a|/dev/emcpower.*|", "r|.*|" ] }'
NOTE
Testing filters using the --config argument will not make permanent changes to the
server's configuration. Make sure to include the working filter in the
/etc/lvm/lvm.conf file after testing.
After configuring an LVM filter, it is recommended that you rebuild the initrd device with the dracut
command so that only the necessary devices are scanned upon reboot.
7.8.3. Duplicate Warnings for Multipath Maps
The following examples show a duplicate PV warning for two devices that are both multipath maps. In
these examples we are not looking at two different paths, but two different devices.
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using
**/dev/mapper/mpatha** not **/dev/mapper/mpathc**
Found duplicate PV GDjTZf7Y03GJHjteqOwrye2dcSCjdaUi: using
**/dev/emcpowera** not **/dev/emcpowerh**
This situation is more serious than duplicate warnings for devices that are both single paths to the same
device, since these warnings often mean that the machine has been presented devices which it should
not be seeing (for example, LUN clones or mirrors). In this case, unless you have a clear idea of what
devices should be removed from the machine, the situation could be unrecoverable. It is recommended
that you contact Red Hat Technical Support to address this issue.
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CHAPTER 8. LVM ADMINISTRATION WITH THE LVM GUI
In addition to the Command Line Interface (CLI), LVM provides a Graphical User Interface (GUI) which
you can use to configure LVM logical volumes. You can open this utility by typing system-configlvm. The LVM chapter of the Storage Administration Guide provides step-by-step instructions for
configuring an LVM logical volume using this utility.
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APPENDIX A. THE DEVICE MAPPER
The Device Mapper is a kernel driver that provides a framework for volume management. It provides a
generic way of creating mapped devices, which may be used as logical volumes. It does not specifically
know about volume groups or metadata formats.
The Device Mapper provides the foundation for a number of higher-level technologies. In addition to
LVM, Device-Mapper multipath and the dmraid command use the Device Mapper. The application
interface to the Device Mapper is the ioctl system call. The user interface is the dmsetup command.
LVM logical volumes are activated using the Device Mapper. Each logical volume is translated into a
mapped device. Each segment translates into a line in the mapping table that describes the device. The
Device Mapper supports a variety of mapping targets, including linear mapping, striped mapping, and
error mapping. So, for example, two disks may be concatenated into one logical volume with a pair of
linear mappings, one for each disk. When LVM creates a volume, it creates an underlying devicemapper device that can be queried with the dmsetup command. For information about the format of
devices in a mapping table, see Section A.1, “Device Table Mappings”. For information about using the
dmsetup command to query a device, see Section A.2, “The dmsetup Command”.
A.1. DEVICE TABLE MAPPINGS
A mapped device is defined by a table that specifies how to map each range of logical sectors of the
device using a supported Device Table mapping. The table for a mapped device is constructed from a
list of lines of the form:
start length mapping [mapping_parameters...]
In the first line of a Device Mapper table, the start parameter must equal 0. The start + length
parameters on one line must equal the start on the next line. Which mapping parameters are specified
in a line of the mapping table depends on which mapping type is specified on the line.
Sizes in the Device Mapper are always specified in sectors (512 bytes).
When a device is specified as a mapping parameter in the Device Mapper, it can be referenced by the
device name in the filesystem (for example, /dev/hda) or by the major and minor numbers in the
format major:minor. The major:minor format is preferred because it avoids pathname lookups.
The following shows a sample mapping table for a device. In this table there are four linear targets:
0 35258368 linear
35258368 35258368
70516736 17694720
88211456 17694720
8:48 65920
linear 8:32 65920
linear 8:16 17694976
linear 8:16 256
The first 2 parameters of each line are the segment starting block and the length of the segment. The
next keyword is the mapping target, which in all of the cases in this example is linear. The rest of the
line consists of the parameters for a linear target.
The following subsections describe these mapping formats:
linear
striped
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mirror
snapshot and snapshot-origin
error
zero
multipath
crypt
device-mapper RAID
thin
thin-pool
A.1.1. The linear Mapping Target
A linear mapping target maps a continuous range of blocks onto another block device. The format of a
linear target is as follows:
start length linear device offset
start
starting block in virtual device
length
length of this segment
device
block device, referenced by the device name in the filesystem or by the major and minor numbers in
the format major:minor
offset
starting offset of the mapping on the device
The following example shows a linear target with a starting block in the virtual device of 0, a segment
length of 1638400, a major:minor number pair of 8:2, and a starting offset for the device of 41146992.
0 16384000 linear 8:2 41156992
The following example shows a linear target with the device parameter specified as the device
/dev/hda.
0 20971520 linear /dev/hda 384
A.1.2. The striped Mapping Target
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APPENDIX A. THE DEVICE MAPPER
The striped mapping target supports striping across physical devices. It takes as arguments the number
of stripes and the striping chunk size followed by a list of pairs of device name and sector. The format of
a striped target is as follows:
start length striped #stripes chunk_size device1 offset1 ... deviceN
offsetN
There is one set of device and offset parameters for each stripe.
start
starting block in virtual device
length
length of this segment
#stripes
number of stripes for the virtual device
chunk_size
number of sectors written to each stripe before switching to the next; must be power of 2 at least as
big as the kernel page size
device
block device, referenced by the device name in the filesystem or by the major and minor numbers in
the format major:minor.
offset
starting offset of the mapping on the device
The following example shows a striped target with three stripes and a chunk size of 128:
0 73728 striped 3 128 8:9 384 8:8 384 8:7 9789824
0
starting block in virtual device
73728
length of this segment
striped 3 128
stripe across three devices with chunk size of 128 blocks
8:9
major:minor numbers of first device
384
starting offset of the mapping on the first device
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8:8
major:minor numbers of second device
384
starting offset of the mapping on the second device
8:7
major:minor numbers of third device
9789824
starting offset of the mapping on the third device
The following example shows a striped target for 2 stripes with 256 KiB chunks, with the device
parameters specified by the device names in the file system rather than by the major and minor
numbers.
0 65536 striped 2 512 /dev/hda 0 /dev/hdb 0
A.1.3. The mirror Mapping Target
The mirror mapping target supports the mapping of a mirrored logical device. The format of a mirrored
target is as follows:
start length mirror log_type #logargs logarg1 ... logargN #devs device1
offset1 ... deviceN offsetN
start
starting block in virtual device
length
length of this segment
log_type
The possible log types and their arguments are as follows:
core
The mirror is local and the mirror log is kept in core memory. This log type takes 1 - 3 arguments:
regionsize [[no]sync] [block_on_error]
disk
The mirror is local and the mirror log is kept on disk. This log type takes 2 - 4 arguments:
logdevice regionsize [[no]sync] [block_on_error]
clustered_core
The mirror is clustered and the mirror log is kept in core memory. This log type takes 2 - 4
arguments:
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APPENDIX A. THE DEVICE MAPPER
regionsize UUID [[no]sync] [block_on_error]
clustered_disk
The mirror is clustered and the mirror log is kept on disk. This log type takes 3 - 5 arguments:
logdevice regionsize UUID [[no]sync] [block_on_error]
LVM maintains a small log which it uses to keep track of which regions are in sync with the mirror or
mirrors. The regionsize argument specifies the size of these regions.
In a clustered environment, the UUID argument is a unique identifier associated with the mirror log
device so that the log state can be maintained throughout the cluster.
The optional [no]sync argument can be used to specify the mirror as "in-sync" or "out-of-sync". The
block_on_error argument is used to tell the mirror to respond to errors rather than ignoring them.
#log_args
number of log arguments that will be specified in the mapping
logargs
the log arguments for the mirror; the number of log arguments provided is specified by the #logargs parameter and the valid log arguments are determined by the log_type parameter.
#devs
the number of legs in the mirror; a device and an offset is specified for each leg
device
block device for each mirror leg, referenced by the device name in the filesystem or by the major and
minor numbers in the format major:minor. A block device and offset is specified for each mirror leg,
as indicated by the #devs parameter.
offset
starting offset of the mapping on the device. A block device and offset is specified for each mirror leg,
as indicated by the #devs parameter.
The following example shows a mirror mapping target for a clustered mirror with a mirror log kept on
disk.
0 52428800 mirror clustered_disk 4 253:2 1024 UUID block_on_error 3 253:3
0 253:4 0 253:5 0
0
starting block in virtual device
52428800
length of this segment
mirror clustered_disk
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mirror target with a log type specifying that mirror is clustered and the mirror log is maintained on disk
4
4 mirror log arguments will follow
253:2
major:minor numbers of log device
1024
region size the mirror log uses to keep track of what is in sync
UUID
UUID of mirror log device to maintain log information throughout a cluster
block_on_error
mirror should respond to errors
3
number of legs in mirror
253:3 0 253:4 0 253:5 0
major:minor numbers and offset for devices constituting each leg of mirror
A.1.4. The snapshot and snapshot-origin Mapping Targets
When you create the first LVM snapshot of a volume, four Device Mapper devices are used:
1. A device with a linear mapping containing the original mapping table of the source volume.
2. A device with a linear mapping used as the copy-on-write (COW) device for the source
volume; for each write, the original data is saved in the COW device of each snapshot to keep its
visible content unchanged (until the COW device fills up).
3. A device with a snapshot mapping combining #1 and #2, which is the visible snapshot volume.
4. The "original" volume (which uses the device number used by the original source volume),
whose table is replaced by a "snapshot-origin" mapping from device #1.
A fixed naming scheme is used to create these devices, For example, you might use the following
commands to create an LVM volume named base and a snapshot volume named snap based on that
volume.
# lvcreate -L 1G -n base volumeGroup
# lvcreate -L 100M --snapshot -n snap volumeGroup/base
This yields four devices, which you can view with the following commands:
# dmsetup table|grep volumeGroup
volumeGroup-base-real: 0 2097152 linear 8:19 384
volumeGroup-snap-cow: 0 204800 linear 8:19 2097536
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volumeGroup-snap: 0 2097152 snapshot 254:11 254:12 P 16
volumeGroup-base: 0 2097152 snapshot-origin 254:11
# ls -lL /dev/mapper/volumeGroup-*
brw------- 1 root root 254, 11 29
real
brw------- 1 root root 254, 12 29
cow
brw------- 1 root root 254, 13 29
brw------- 1 root root 254, 10 29
ago 18:15 /dev/mapper/volumeGroup-baseago 18:15 /dev/mapper/volumeGroup-snapago 18:15 /dev/mapper/volumeGroup-snap
ago 18:14 /dev/mapper/volumeGroup-base
The format for the snapshot-origin target is as follows:
start length snapshot-origin origin
start
starting block in virtual device
length
length of this segment
origin
base volume of snapshot
The snapshot-origin will normally have one or more snapshots based on it. Reads will be mapped
directly to the backing device. For each write, the original data will be saved in the COW device of each
snapshot to keep its visible content unchanged until the COW device fills up.
The format for the snapshot target is as follows:
start length snapshot origin COW-device P|N chunksize
start
starting block in virtual device
length
length of this segment
origin
base volume of snapshot
COW-device
Device on which changed chunks of data are stored
P|N
P (Persistent) or N (Not persistent); indicates whether snapshot will survive after reboot. For transient
snapshots (N) less metadata must be saved on disk; they can be kept in memory by the kernel.
chunksize
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Size in sectors of changed chunks of data that will be stored on the COW device
The following example shows a snapshot-origin target with an origin device of 254:11.
0 2097152 snapshot-origin 254:11
The following example shows a snapshot target with an origin device of 254:11 and a COW device of
254:12. This snapshot device is persistent across reboots and the chunk size for the data stored on the
COW device is 16 sectors.
0 2097152 snapshot 254:11 254:12 P 16
A.1.5. The error Mapping Target
With an error mapping target, any I/O operation to the mapped sector fails.
An error mapping target can be used for testing. To test how a device behaves in failure, you can create
a device mapping with a bad sector in the middle of a device, or you can swap out the leg of a mirror and
replace the leg with an error target.
An error target can be used in place of a failing device, as a way of avoiding timeouts and retries on the
actual device. It can serve as an intermediate target while you rearrange LVM metadata during failures.
The error mapping target takes no additional parameters besides the start and length parameters.
The following example shows an error target.
0 65536 error
A.1.6. The zero Mapping Target
The zero mapping target is a block device equivalent of /dev/zero. A read operation to this mapping
returns blocks of zeros. Data written to this mapping is discarded, but the write succeeds. The zero
mapping target takes no additional parameters besides the start and length parameters.
The following example shows a zero target for a 16Tb Device.
0 65536 zero
A.1.7. The multipath Mapping Target
The multipath mapping target supports the mapping of a multipathed device. The format for the
multipath target is as follows:
start length multipath #features [feature1 ... featureN] #handlerargs
[handlerarg1 ... handlerargN] #pathgroups pathgroup pathgroupargs1 ...
pathgroupargsN
There is one set of pathgroupargs parameters for each path group.
start
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APPENDIX A. THE DEVICE MAPPER
starting block in virtual device
length
length of this segment
#features
The number of multipath features, followed by those features. If this parameter is zero, then there is
no feature parameter and the next device mapping parameter is #handlerargs. Currently there is
one supported feature that can be set with the features attribute in the multipath.conf file,
queue_if_no_path. This indicates that this multipathed device is currently set to queue I/O
operations if there is no path available.
In the following example, the no_path_retry attribute in the multipath.conf file has been set to
queue I/O operations only until all paths have been marked as failed after a set number of attempts
have been made to use the paths. In this case, the mapping appears as follows until all the path
checkers have failed the specified number of checks.
0 71014400 multipath 1 queue_if_no_path 0 2 1 round-robin 0 2 1 66:128 \
1000 65:64 1000 round-robin 0 2 1 8:0 1000 67:192 1000
After all the path checkers have failed the specified number of checks, the mapping would appear as
follows.
0 71014400 multipath 0 0 2 1 round-robin 0 2 1 66:128 1000 65:64 1000 \
round-robin 0 2 1 8:0 1000 67:192 1000
#handlerargs
The number of hardware handler arguments, followed by those arguments. A hardware handler
specifies a module that will be used to perform hardware-specific actions when switching path groups
or handling I/O errors. If this is set to 0, then the next parameter is #pathgroups.
#pathgroups
The number of path groups. A path group is the set of paths over which a multipathed device will load
balance. There is one set of pathgroupargs parameters for each path group.
pathgroup
The next path group to try.
pathgroupsargs
Each path group consists of the following arguments:
pathselector #selectorargs #paths #pathargs device1 ioreqs1 ... deviceN
ioreqsN
There is one set of path arguments for each path in the path group.
pathselector
Specifies the algorithm in use to determine what path in this path group to use for the next I/O
operation.
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#selectorargs
The number of path selector arguments which follow this argument in the multipath mapping.
Currently, the value of this argument is always 0.
#paths
The number of paths in this path group.
#pathargs
The number of path arguments specified for each path in this group. Currently this number is
always 1, the ioreqs argument.
device
The block device number of the path, referenced by the major and minor numbers in the format
major:minor
ioreqs
The number of I/O requests to route to this path before switching to the next path in the current
group.
Figure A.1, “Multipath Mapping Target” shows the format of a multipath target with two path groups.
Figure A.1. Multipath Mapping Target
The following example shows a pure failover target definition for the same multipath device. In this target
there are four path groups, with only one open path per path group so that the multipathed device will
use only one path at a time.
0 71014400 multipath 0 0 4 1 round-robin 0 1 1 66:112 1000 \
round-robin 0 1 1 67:176 1000 round-robin 0 1 1 68:240 1000 \
round-robin 0 1 1 65:48 1000
The following example shows a full spread (multibus) target definition for the same multipathed device.
In this target there is only one path group, which includes all of the paths. In this setup, multipath spreads
the load evenly out to all of the paths.
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APPENDIX A. THE DEVICE MAPPER
0 71014400 multipath 0 0 1 1 round-robin 0 4 1 66:112 1000 \
67:176 1000 68:240 1000 65:48 1000
For further information about multipathing, see the Using Device Mapper Multipath document.
A.1.8. The crypt Mapping Target
The crypt target encrypts the data passing through the specified device. It uses the kernel Crypto API.
The format for the crypt target is as follows:
start length crypt cipher key IV-offset device offset
start
starting block in virtual device
length
length of this segment
cipher
Cipher consists of cipher[-chainmode]-ivmode[:iv options].
cipher
Ciphers available are listed in /proc/crypto (for example, aes).
chainmode
Always use cbc. Do not use ebc; it does not use an initial vector (IV).
ivmode[:iv options]
IV is an initial vector used to vary the encryption. The IV mode is plain or essiv:hash. An
ivmode of -plain uses the sector number (plus IV offset) as the IV. An ivmode of -essiv is an
enhancement avoiding a watermark weakness.
key
Encryption key, supplied in hex
IV-offset
Initial Vector (IV) offset
device
block device, referenced by the device name in the filesystem or by the major and minor numbers in
the format major:minor
offset
starting offset of the mapping on the device
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The following is an example of a crypt target.
0 2097152 crypt aes-plain 0123456789abcdef0123456789abcdef 0 /dev/hda 0
A.1.9. The device-mapper RAID Mapping Target
The device-mapper RAID (dm-raid) target provides a bridge from DM to MD. It allows the MD RAID
drivers to be accessed using a device-mapper interface. The format of the dm-raid target is as follows
start length raid raid_type #raid_params raid_params #raid_devs
metadata_dev0 dev0 [.. metadata_devN devN]
start
starting block in virtual device
length
length of this segment
raid_type
The RAID type can be one of the following
raid1
RAID1 mirroring
raid4
RAID4 dedicated parity disk
raid5_la
RAID5 left asymmetric
— rotating parity 0 with data continuation
raid5_ra
RAID5 right asymmetric
— rotating parity N with data continuation
raid5_ls
RAID5 left symmetric
— rotating parity 0 with data restart
raid5_rs
RAID5 right symmetric
— rotating parity N with data restart
raid6_zr
RAID6 zero restart
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APPENDIX A. THE DEVICE MAPPER
— rotating parity 0 (left to right) with data restart
raid6_nr
RAID6 N restart
— rotating parity N (right to left) with data restart
raid6_nc
RAID6 N continue
— rotating parity N (right to left) with data continuation
raid10
Various RAID10-inspired algorithms selected by further optional arguments
— RAID 10: Striped mirrors (striping on top of mirrors)
— RAID 1E: Integrated adjacent striped mirroring
— RAID 1E: Integrated offset striped mirroring
— Other similar RAID10 variants
#raid_params
The number of parameters that follow
raid_params
Mandatory parameters:
chunk_size
Chunk size in sectors. This parameter is often known as "stripe size". It is the only mandatory
parameter and is placed first.
Followed by optional parameters (in any order):
[sync|nosync]
Force or prevent RAID initialization.
rebuild idx
Rebuild drive number idx (first drive is 0).
daemon_sleep ms
Interval between runs of the bitmap daemon that clear bits. A longer interval means less bitmap
I/O but resyncing after a failure is likely to take longer.
min_recovery_rate KB/sec/disk
Throttle RAID initialization
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max_recovery_rate KB/sec/disk
Throttle RAID initialization
write_mostly idx
Mark drive index idx write-mostly.
max_write_behind sectors
See the description of --write-behind in the mdadm man page.
stripe_cache sectors
Stripe cache size (RAID 4/5/6 only)
region_size sectors
The region_size multiplied by the number of regions is the logical size of the array. The bitmap
records the device synchronization state for each region.
raid10_copies #copies
The number of RAID10 copies. This parameter is used in conjunction with the raid10_format
parameter to alter the default layout of a RAID10 configuration. The default value is 2.
raid10_format near|far|offset
This parameter is used in conjunction with the raid10_copies parameter to alter the default
layout of a RAID10 configuration. The default value is near, which specifies a standard mirroring
layout.
If the raid10_copies and raid10_format are left unspecified, or raid10_copies 2 and/or
raid10_format near is specified, then the layouts for 2, 3 and 4 devices are as follows:
2 drives
-------A1 A1
A2 A2
A3 A3
A4 A4
.. ..
3 drives
---------A1 A1 A2
A2 A3 A3
A4 A4 A5
A5 A6 A6
.. .. ..
4 drives
-------------A1 A1 A2 A2
A3 A3 A4 A4
A5 A5 A6 A6
A7 A7 A8 A8
.. .. .. ..
The 2-device layout is equivalent to 2-way RAID1. The 4-device layout is what a traditional
RAID10 would look like. The 3-device layout is what might be called a 'RAID1E - Integrated
Adjacent Stripe Mirroring'.
If raid10_copies 2 and raid10_format far are specified, then the layouts for 2, 3 and 4
devices are as follows:
2 drives
-------A1 A2
A3 A4
A5 A6
.. ..
A2 A1
134
3 drives
----------A1 A2 A3
A4 A5 A6
A7 A8 A9
.. .. ..
A3 A1 A2
4 drives
-----------------A1
A2
A3
A4
A5
A6
A7
A8
A9
A10 A11 A12
..
..
..
..
A2
A1
A4
A3
APPENDIX A. THE DEVICE MAPPER
A4
A6
..
A3
A5
..
A6
A9
..
A4
A7
..
A5
A8
..
A6
A10
..
A5
A9
..
A8
A12
..
A7
A11
..
If raid10_copies 2 and raid10_format offset are specified, then the layouts for 2, 3 and
4 devices are as follows:
2 drives
-------A1 A2
A2 A1
A3 A4
A4 A3
A5 A6
A6 A5
.. ..
3 drives
-------A1 A2 A3
A3 A1 A2
A4 A5 A6
A6 A4 A5
A7 A8 A9
A9 A7 A8
.. .. ..
4 drives
-----------------A1
A2
A3
A4
A2
A1
A4
A3
A5
A6
A7
A8
A6
A5
A8
A7
A9
A10 A11 A12
A10 A9
A12 A11
..
..
..
..
These layouts closely resemble the layouts fo RAID1E - Integrated Offset Stripe Mirroring'
#raid_devs
The number of devices composing the array
Each device consists of two entries. The first is the device containing the metadata (if any); the
second is the one containing the data.
If a drive has failed or is missing at creation time, a '-' can be given for both the metadata and data
drives for a given position.
The following example shows a RAID4 target with a starting block of 0 and a segment length of
1960893648. There are 4 data drives, 1 parity, with no metadata devices specified to hold
superblock/bitmap info and a chunk size of 1MiB
0 1960893648 raid raid4 1 2048 5 - 8:17 - 8:33 - 8:49 - 8:65 - 8:81
The following example shows a RAID4 target with a starting block of 0 and a segment length of
1960893648. there are 4 data drives, 1 parity, with metadata devices, a chunk size of 1MiB, force RAID
initialization, and a min_recovery rate of 20 kiB/sec/disks.
0 1960893648 raid raid4 4 2048 sync min_recovery_rate 20 5 8:17 8:18 8:33
8:34 8:49 8:50 8:65 8:66 8:81 8:82
A.1.10. The thin and thin-pool Mapping Targets
The format of a thin-pool target is as follows:
start length thin-pool metadata_dev data_dev data_block_size
low_water_mark [#feature_args [arg*] ]
start
starting block in virtual device
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Logical Volume Manager Administration
length
length of this segment
metadata_dev
The metadata device
data_dev
The data device
data_block_size
The data block size (in sectors). The data block size gives the smallest unit of disk space that can be
allocated at a time expressed in units of 512-byte sectors. Data block size must be between 64KB
(128 sectors) and 1GB (2097152 sectors) inclusive and it must be a mutlipole of 128 (64KB).
low_water_mark
The low water mark, expressed in blocks of size data_block_size. If free space on the data
device drops below this level then a device-mapper event will be triggered which a user-space
daemon should catch allowing it to extend the pool device. Only one such event will be sent.
Resuming a device with a new table itself triggers an event so the user-space daemon can use this to
detect a situation where a new table already exceeds the threshold.
A low water mark for the metadata device is maintained in the kernel and will trigger a device-mapper
event if free space on the metadata device drops below it.
#feature_args
The number of feature arguments
arg
The thin pool feature argument are as follows:
skip_block_zeroing
Skip the zeroing of newly-provisioned blocks.
ignore_discard
Disable discard support.
no_discard_passdown
Do not pass discards down to the underlying data device, but just remove the mapping.
read_only
Do not allow any changes to be made to the pool metadata.
error_if_no_space
Error IOs, instead of queuing, if no space.
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APPENDIX A. THE DEVICE MAPPER
The following example shows a thin-pool target with a starting block in the virtual device of 0, a segment
length of 1638400. /dev/sdc1 is a small metadata device and /dev/sdc2 is a larger data device. The
chunksize is 64k, the low_water_mark is 0, and there are no features.
0 16384000 thin-pool /dev/sdc1 /dev/sdc2 128 0 0
The format of a thin target is as follows:
start length thin pool_dev dev_id [external_origin_dev]
start
starting block in virtual device
length
length of this segment
pool_dev
The thin-pool device, for example /dev/mapper/my_pool or 253:0
dev_id
The internal device identifier of the device to be activated.
external_origin_dev
An optional block device outside the pool to be treated as a read-only snapshot origin. Reads to
unprovisioned areas of the thin target will be mapped to this device.
The following example shows a 1 GiB thinLV that uses /dev/mapper/pool as its backing store (thinpool). The target has a starting block in the virtual device of 0 and a segment length of 2097152.
0 2097152 thin /dev/mapper/pool 1
A.2. THE DMSETUP COMMAND
The dmsetup command is a command line wrapper for communication with the Device Mapper. For
general system information about LVM devices, you may find the info, ls, status, and deps options
of the dmsetup command to be useful, as described in the following subsections.
For information about additional options and capabilities of the dmsetup command, see the dmsetup(8)
man page.
A.2.1. The dmsetup info Command
The dmsetup info device command provides summary information about Device Mapper devices. If
you do not specify a device name, the output is information about all of the currently configured Device
Mapper devices. If you specify a device, then this command yields information for that device only.
The dmsetup info command provides information in the following categories:
Name
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Logical Volume Manager Administration
The name of the device. An LVM device is expressed as the volume group name and the logical
volume name separated by a hyphen. A hyphen in the original name is translated to two hyphens.
During standard LVM operations, you should not use the name of an LVM device in this format to
specify an LVM device directly, but instead you should use the vg/lv alternative.
State
Possible device states are SUSPENDED, ACTIVE, and READ-ONLY. The dmsetup suspend
command sets a device state to SUSPENDED. When a device is suspended, all I/O operations to that
device stop. The dmsetup resume command restores a device state to ACTIVE.
Read Ahead
The number of data blocks that the system reads ahead for any open file on which read operations
are ongoing. By default, the kernel chooses a suitable value automatically. You can change this value
with the --readahead option of the dmsetup command.
Tables present
Possible states for this category are LIVE and INACTIVE. An INACTIVE state indicates that a table
has been loaded which will be swapped in when a dmsetup resume command restores a device
state to ACTIVE, at which point the table's state becomes LIVE. For information, see the dmsetup
man page.
Open count
The open reference count indicates how many times the device is opened. A mount command opens
a device.
Event number
The current number of events received. Issuing a dmsetup wait n command allows the user to
wait for the n'th event, blocking the call until it is received.
Major, minor
Major and minor device number
Number of targets
The number of fragments that make up a device. For example, a linear device spanning 3 disks
would have 3 targets. A linear device composed of the beginning and end of a disk, but not the middle
would have 2 targets.
UUID
UUID of the device.
The following example shows partial output for the dmsetup info command.
# dmsetup info
Name:
State:
Read Ahead:
Tables present:
Open count:
Event number:
138
testgfsvg-testgfslv1
ACTIVE
256
LIVE
0
0
APPENDIX A. THE DEVICE MAPPER
Major, minor:
253, 2
Number of targets: 2
UUID: LVM-K528WUGQgPadNXYcFrrf9LnPlUMswgkCkpgPIgYzSvigM7SfeWCypddNSWtNzc2N
...
Name:
VolGroup00-LogVol00
State:
ACTIVE
Read Ahead:
256
Tables present:
LIVE
Open count:
1
Event number:
0
Major, minor:
253, 0
Number of targets: 1
UUID: LVM-tOcS1kqFV9drb0X1Vr8sxeYP0tqcrpdegyqj5lZxe45JMGlmvtqLmbLpBcenh2L3
A.2.2. The dmsetup ls Command
You can list the device names of mapped devices with the dmsetup ls command. You can list devices
that have at least one target of a specified type with the dmsetup ls --target target_type
command. For other options of the dmsetup ls, see the dmsetup man page.
The following example shows the command to list the device names of currently configured mapped
devices.
# dmsetup ls
testgfsvg-testgfslv3
testgfsvg-testgfslv2
testgfsvg-testgfslv1
VolGroup00-LogVol01
VolGroup00-LogVol00
(253:4)
(253:3)
(253:2)
(253:1)
(253:0)
The following example shows the command to list the devices names of currently configured mirror
mappings.
# dmsetup ls --target mirror
lock_stress-grant--02.1722
lock_stress-grant--01.1720
lock_stress-grant--03.1718
lock_stress-grant--02.1716
lock_stress-grant--03.1713
lock_stress-grant--02.1709
lock_stress-grant--01.1707
lock_stress-grant--01.1724
lock_stress-grant--03.1711
(253,
(253,
(253,
(253,
(253,
(253,
(253,
(253,
(253,
34)
18)
52)
40)
47)
23)
8)
14)
27)
LVM configurations that are stacked on multipath or other device mapper devices can be complex to sort
out. The dmsetup ls command provides a --tree option that displays dependencies between
devices as a tree, as in the following example.
# dmsetup ls --tree
vgtest-lvmir (253:13)
├─vgtest-lvmir_mimage_1 (253:12)
│ └─mpathep1 (253:8)
│
└─mpathe (253:5)
│
├─ (8:112)
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Logical Volume Manager Administration
│
└─ (8:64)
├─vgtest-lvmir_mimage_0 (253:11)
│ └─mpathcp1 (253:3)
│
└─mpathc (253:2)
│
├─ (8:32)
│
└─ (8:16)
└─vgtest-lvmir_mlog (253:4)
└─mpathfp1 (253:10)
└─mpathf (253:6)
├─ (8:128)
└─ (8:80)
A.2.3. The dmsetup status Command
The dmsetup status device command provides status information for each target in a specified
device. If you do not specify a device name, the output is information about all of the currently configured
Device Mapper devices. You can list the status only of devices that have at least one target of a specified
type with the dmsetup status --target target_type command.
The following example shows the command to list the status of the targets in all currently configured
mapped devices.
# dmsetup status
testgfsvg-testgfslv3: 0 312352768 linear
testgfsvg-testgfslv2: 0 312352768 linear
testgfsvg-testgfslv1: 0 312352768 linear
testgfsvg-testgfslv1: 312352768 50331648 linear
VolGroup00-LogVol01: 0 4063232 linear
VolGroup00-LogVol00: 0 151912448 linear
A.2.4. The dmsetup deps Command
The dmsetup deps device command provides a list of (major, minor) pairs for devices referenced
by the mapping table for the specified device. If you do not specify a device name, the output is
information about all of the currently configured Device Mapper devices.
The following example shows the command to list the dependencies of all currently configured mapped
devices.
# dmsetup deps
testgfsvg-testgfslv3: 1 dependencies
testgfsvg-testgfslv2: 1 dependencies
testgfsvg-testgfslv1: 1 dependencies
VolGroup00-LogVol01: 1 dependencies
VolGroup00-LogVol00: 1 dependencies
:
:
:
:
:
(8,
(8,
(8,
(8,
(8,
16)
16)
16)
2)
2)
The following example shows the command to list the dependencies only of the device lock_stressgrant--02.1722:
# dmsetup deps lock_stress-grant--02.1722
3 dependencies : (253, 33) (253, 32) (253, 31)
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APPENDIX A. THE DEVICE MAPPER
A.3. DEVICE MAPPER SUPPORT FOR THE UDEV DEVICE MANAGER
The primary role of the udev device manager is to provide a dynamic way of setting up nodes in the
/dev directory. The creation of these nodes is directed by the application of udev rules in user space.
These rules are processed on udev events sent from the kernel directly as a result of adding, removing
or changing particular devices. This provides a convenient and central mechanism for hotplugging
support.
Besides creating the actual nodes, the udev device manager is able to create symbolic links which the
user can name. This provides users the freedom to choose their own customized naming and directory
structure in the/dev directory, if needed.
Each udev event contains basic information about the device being processed, such as its name, the
subsystem it belongs to, the device's type, its major and minor number used, and the type of the event.
Given that, and having the possibility of accessing all the information found in the /sys directory that is
also accessible within udev rules, the users are able to utilize simple filters based on this information and
run the rules conditionally based on this information.
The udev device manager also provides a centralized way of setting up the nodes' permissions. A user
can easily add a customized set of rules to define the permissions for any device specified by any bit of
information that is available while processing the event.
It is also possible to add program hooks in udev rules directly. The udev device manager can call these
programs to provide further processing that is needed to handle the event. Also, the program can export
environment variables as a result of this processing. Any results given can be used further in the rules as
a supplementary source of information.
Any software using the udev library is able to receive and process udev events with all the information
that is available, so the processing is not bound to the udev daemon only.
A.3.1. udev Integration with the Device Mapper
In Red Hat Enterprise Linux 6, the Device Mapper provides direct support for udev integration. This
synchronizes the Device Mapper with all udev processing related to Device Mapper devices, including
LVM devices. The synchronization is needed since the rule application in the udev daemon is a form of
parallel processing with the program that is the source of the device's changes (such as dmsetup and
LVM). Without this support, it was a common problem for a user to try to remove a device that was still
open and processed by udev rules as a result of a previous change event; this was particularly common
when there was a very short time between changes for that device.
The Red Hat Enterprise Linux 6 release provides officially supported udev rules for Device Mapper
devices in general and for LVM as well. Table A.1, “udev Rules for Device-Mapper Devices” summarizes
these rules, which are installed in /lib/udev/rules.d.
Table A.1. udev Rules for Device-Mapper Devices
Filename
Description
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Filename
10-dm.rules
Description
Contains basic/general Device Mapper rules and creates the symlinks
in /dev/mapper with a
/dev/dm-N target where N is a
number assigned dynamically to a device by the kernel
(/dev/dm-N is a node)
NOTE: /dev/dm-N nodes should never be used in scripts to
access the device since the N number is assigned dynamically and
changes with the sequence of how devices are activated. Therefore,
true names in the /dev/mapper directory should be used. This
layout is to support udev requirements of how nodes/symlinks should
be created.
11-dm-lvm.rules
Contains rules applied for LVM devices and creates the symlinks for
the volume group's logical volumes. The symlinks are created in the
/dev/vgname directory with a /dev/dm-N target.
NOTE: To be consistent with the standard for naming all future rules
for Device Mapper subsystems, udev rules should follow the format
11-dm-subsystem_name.rules . Any libdevmapper
users providing udev rules as well should follow this standard.
13-dm-disk.rules
Contains rules to be applied for all Device Mapper devices in
general and creates symlinks in the /dev/disk/by-id,
/dev/disk/by-uuid and the /dev/disk/by-uuid
directories.
95-dm-notify.rules
Contains the rule to notify the waiting process using
libdevmapper (just like LVM and dmsetup). The notification is
done after all previous rules are applied, to ensure any udev
processing is complete. Notified process is then resumed.
69-dm-lvm-metad.rules
Contains a hook to trigger an LVM scan on any newly appeared
block device in the system and do any LVM autoactivation if
possible. This supports the lvmetad daemon, which is set with
use_lvmetad=1 in the lvm.conf file. The lvmeetad
daemon and autoactivation are not supported in a clustered
environment.
You can add additional customized permission rules by means of the 12-dm-permissions.rules
file. This file is not installed in the /lib/udev/rules directory; it is found in the
/usr/share/doc/device-mapper-version directory. The 12-dm-permissions.rules file is a
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APPENDIX A. THE DEVICE MAPPER
template containing hints for how to set the permissions, based on some matching rules given as an
example; the file contains examples for some common situations. You can edit this file and place it
manually in the /etc/udev/rules.d directory where it will survive updates, so the settings will remain.
These rules set all basic variables that could be used by any other rules while processing the events.
The following variables are set in 10-dm.rules:
DM_NAME: Device Mapper device name
DM_UUID: Device Mapper device UUID
DM_SUSPENDED: the suspended state of Device Mapper device
DM_UDEV_RULES_VSN: udev rules version (this is primarily for all other rules to check that
previously mentioned variables are set directly by official Device Mapper rules)
The following variables are set in 11-dm-lvm.rules:
DM_LV_NAME: logical volume name
DM_VG_NAME: volume group name
DM_LV_LAYER: LVM layer name
All these variables can be used in the 12-dm-permissions.rules file to define a permission for
specific Device Mapper devices, as documented in the 12-dm-permissions.rules file.
A.3.2. Commands and Interfaces that Support udev
Table A.2, “dmsetup Commands to Support udev” summarizes the dmsetup commands that support
udev integration.
Table A.2. dmsetup Commands to Support udev
Command
Description
dmsetup udevcomplete
Used to notify that udev has completed processing the rules and
unlocks waiting process (called from within udev rules in 95-dmnotify.rules).
dmsetup udevcomplete_all
Used for debugging purposes to manually unlock all waiting
processes.
dmsetup udevcookies
Used for debugging purposes, to show all existing cookies (systemwide semaphores).
dmsetup udevcreatecookie
Used to create a cookie (semaphore) manually. This is useful to run
more processes under one synchronization resource.
dmsetup udevreleasecookie
Used to wait for all udev processing related to all processes put
under that one synchronization cookie.
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The dmsetup options that support udev integration are as follows.
--udevcookie
Needs to be defined for all dmsetup processes we would like to add into a udev transaction. It is used
in conjunction with udevcreatecookie and udevreleasecookie:
COOKIE=$(dmsetup udevcreatecookie)
dmsetup command --udevcookie $COOKIE
dmsetup command --udevcookie $COOKIE
....
dmsetup command --udevcookie $COOKIE
dmsetup udevreleasecookie --udevcookie
....
....
....
$COOKIE
Besides using the --udevcookie option, you can just export the variable into an environment of the
process:
export DM_UDEV_COOKIE=$(dmsetup udevcreatecookie)
dmsetup command ...
dmsetup command ...
...
dmsetup command ...
--noudevrules
Disables udev rules. Nodes/symlinks will be created by libdevmapper itself (the old way). This
option is for debugging purposes, if udev does not work correctly.
--noudevsync
Disables udev synchronization. This is also for debugging purposes.
For more information on the dmsetup and its options, see the dmsetup(8) man page.
The LVM commands support the following options that support udev integration:
--noudevrules: as for the dmsetup command, disables udev rules.
--noudevsync: as for the dmsetup command, disables udev synchronization.
The lvm.conf file includes the following options that support udev integration:
udev_rules: enables/disables udev_rules for all LVM2 commands globally.
udev_sync: enables/disables udev synchronization for all LVM commands globally.
For more information on the lvm.conf file options, see the inline comments in the lvm.conf file.
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APPENDIX B. THE LVM CONFIGURATION FILES
APPENDIX B. THE LVM CONFIGURATION FILES
LVM supports multiple configuration files. At system startup, the lvm.conf configuration file is loaded
from the directory specified by the environment variable LVM_SYSTEM_DIR, which is set to /etc/lvm
by default.
The lvm.conf file can specify additional configuration files to load. Settings in later files override
settings from earlier ones. To display the settings in use after loading all the configuration files, execute
the lvmconfig command.
For information on loading additional configuration files, see Section D.2, “Host Tags”.
B.1. THE LVM CONFIGURATION FILES
The following files are used for LVM configuration:
/etc/lvm/lvm.conf
Central configuration file read by the tools.
etc/lvm/lvm_hosttag.conf
For each host tag, an extra configuration file is read if it exists: lvm_hosttag.conf. If that file
defines new tags, then further configuration files will be appended to the list of files to read in. For
information on host tags, see Section D.2, “Host Tags”.
LVM profiles
An LVM profile is a set of selected customizable configuration settings that can be implemented for
specific environments. The settings in an LVM profile can be used to override existing configuration.
For information on LVM profiles see Section B.3, “LVM Profiles”.
In addition to the LVM configuration files, a system running LVM includes the following files that affect
LVM system setup:
/etc/lvm/cache/.cache
Device name filter cache file (configurable).
/etc/lvm/backup/
Directory for automatic volume group metadata backups (configurable).
/etc/lvm/archive/
Directory for automatic volume group metadata archives (configurable with regard to directory path
and archive history depth).
/var/lock/lvm/
In single-host configuration, lock files to prevent parallel tool runs from corrupting the metadata; in a
cluster, cluster-wide DLM is used.
B.2. THE LVMCONFIG COMMAND
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You can display the current LVM configuration, or save the configuration to a file, with the lvmconfig
command. The lvmconfig command displays the LVM configuration information after loading the
/etc/lvm/lvm.conf file and any other configuration files.
There are a variety of features that the lvmconfig command provides, including the following;
You can dump the current lvm configuration merged with any tag configuration files.
You can dump all current configuration settings for which the values differ from the defaults.
You can dump all new configuration settings introduced in the current LVM version, in a specific
LVM version.
You can dump all profilable configuration settings, either in their entirety or separately for
command and metadata profiles. For information on LVM profiles see Section B.3, “LVM
Profiles”.
You can dump only the configuration settings for a specific version of LVM.
You can validate the current configuration.
For a full list of supported features and information on specifying the lvmconfig options, see the
lvmconfig man page.
B.3. LVM PROFILES
An LVM profile is a set of selected customizable configuration settings that can be used to achieve
certain characteristics in various environments or uses. Normally, the name of the profile should reflect
that environment or use. An LVM profile overrides existing configuration.
There are two groups of LVM profiles that LVM recognizes: command profiles and metadata profiles.
A command profile is used to override selected configuration settings at the global LVM
command level. The profile is applied at the beginning of LVM command execution and it is used
throughout the time of the LVM command execution. You apply a command profile by specifying
the --commandprofile ProfileName option when executing an LVM command.
A metadata profile is used to override selected configuration settings at the volume group/logical
volume level. It is applied independently for each volume group/logical volume that is being
processed. As such, each volume group/logical volume can store the profile name used in its
metadata so that next time the volume group/logical volume is processed, the profile is applied
automatically. If the volume group and any of its logical volumes have different profiles defined,
the profile defined for the logical volume is preferred.
You can attach a metadata profile to a volume group or logical volume by specifying the -metadataprofile ProfileName option when you create the volume group or logical
volume with the vgcreate or lvcreate command.
You can attach or detach a metadata profile to an existing volume group or logical volume
by specifying the --metadataprofile ProfileName or the --detachprofile option
of the lvchange or vgchange command.
You can specify the -o vg_profile and -o lv_profile output options of the vgs and
lvs commands to display the metadata profile currently attached to a volume group or a
logical volume.
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APPENDIX B. THE LVM CONFIGURATION FILES
The set of options allowed for command profiles and the set of options allowed for metadata profiles are
mutually exclusive. The settings that belong to either of these two sets cannot be mixed together and the
LVM tools will reject such profiles.
LVM provides a few predefined configuration profiles. The LVM profiles are stored in the
/etc/lvm/profile directory by default. This location can be changed by using the profile_dir
setting in the /etc/lvm/lvm.conf file. Each profile configuration is stored in ProfileName.profile file in
the profile directory. When referencing the profile in an LVM command, the .profile suffix is
omitted.
You can create additional profiles with different values. For this purpose, LVM provides the
command_profile_template.profile file (for command profiles) and the
metadata_profile_template.profile file (for metadata profiles) which contain all settings that
are customizable by profiles of each type. You can copy these template profiles and edit them as
needed.
Alternatively, you can use the lvmconfig command to generate a new profile for a given section of the
profile file for either profile type. The following command creates a new command profile named
ProfileName.profile consisting of the settings in section.
lvmconfig --file ProfileName.profile --type profilable-command section
The following command creates a new metadata profile named ProfileName.profile consisting of the
settings in section.
lvmconfig --file ProfileName.profile --type profilable-metadata section
If the section is not specified, all profilable settings are reported.
B.4. SAMPLE LVM.CONF FILE
The following is a sample lvm.conf configuration file. Your configuration file may differ slightly from this
one.
NOTE
You can generate an lvm.conf file with all of the default values set and with the
comments included by running the following command:
lvmconfig --type default --withcomments
# This is an example configuration file for the LVM2 system.
# It contains the default settings that would be used if there was no
# /etc/lvm/lvm.conf file.
#
# Refer to 'man lvm.conf' for further information including the file
layout.
#
# To put this file in a different directory and override /etc/lvm set
# the environment variable LVM_SYSTEM_DIR before running the tools.
#
# N.B. Take care that each setting only appears once if uncommenting
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# example settings in this file.
# This section allows you to set the way the configuration settings are
handled.
config {
# If enabled, any LVM2 configuration mismatch is reported.
# This implies checking that the configuration key is understood
# by LVM2 and that the value of the key is of a proper type.
# If disabled, any configuration mismatch is ignored and default
# value is used instead without any warning (a message about the
# configuration key not being found is issued in verbose mode only).
checks = 1
# If enabled, any configuration mismatch aborts the LVM2 process.
abort_on_errors = 0
# Directory where LVM looks for configuration profiles.
profile_dir = "/etc/lvm/profile"
}
# This section allows you to configure which block devices should
# be used by the LVM system.
devices {
# Where do you want your volume groups to appear ?
dir = "/dev"
# An array of directories that contain the device nodes you wish
# to use with LVM2.
scan = [ "/dev" ]
# If set, the cache of block device nodes with all associated symlinks
# will be constructed out of the existing udev database content.
# This avoids using and opening any inapplicable non-block devices or
# subdirectories found in the device directory. This setting is
applied
# to udev-managed device directory only, other directories will be
scanned
# fully. LVM2 needs to be compiled with udev support for this setting
to
# take effect. N.B. Any device node or symlink not managed by udev in
# udev directory will be ignored with this setting on.
obtain_device_list_from_udev = 1
#
#
#
#
#
If several entries in the scanned directories correspond to the
same block device and the tools need to display a name for device,
all the pathnames are matched against each item in the following
list of regular expressions in turn and the first match is used.
preferred_names = [ ]
# Try to avoid using undescriptive /dev/dm-N names, if present.
preferred_names = [ "^/dev/mpath/", "^/dev/mapper/mpath",
"^/dev/[hs]d" ]
# A filter that tells LVM2 to only use a restricted set of devices.
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APPENDIX B. THE LVM CONFIGURATION FILES
#
#
#
#
#
#
The filter consists of an array of regular expressions. These
expressions can be delimited by a character of your choice, and
prefixed with either an 'a' (for accept) or 'r' (for reject).
The first expression found to match a device name determines if
the device will be accepted or rejected (ignored). Devices that
don't match any patterns are accepted.
# Be careful if there there are symbolic links or multiple filesystem
# entries for the same device as each name is checked separately
against
# the list of patterns. The effect is that if the first pattern in
the
# list to match a name is an 'a' pattern for any of the names, the
device
# is accepted; otherwise if the first pattern in the list to match a
name
# is an 'r' pattern for any of the names it is rejected; otherwise it
is
# accepted.
# Don't have more than one filter line active at once: only one gets
used.
# Run vgscan after you change this parameter to ensure that
# the cache file gets regenerated (see below).
# If it doesn't do what you expect, check the output of 'vgscan vvvv'.
# By default we accept every block device:
filter = [ "a/.*/" ]
# Exclude the cdrom drive
# filter = [ "r|/dev/cdrom|" ]
# When testing I like to work with just loopback devices:
# filter = [ "a/loop/", "r/.*/" ]
# Or maybe all loops and ide drives except hdc:
# filter =[ "a|loop|", "r|/dev/hdc|", "a|/dev/ide|", "r|.*|" ]
# Use anchors if you want to be really specific
# filter = [ "a|^/dev/hda8$|", "r/.*/" ]
# Since "filter" is often overridden from command line, it is not
suitable
# for system-wide device filtering (udev rules, lvmetad). To hide
devices
# from LVM-specific udev processing and/or from lvmetad, you need to
set
# global_filter. The syntax is the same as for normal "filter"
# above. Devices that fail the global_filter are not even opened by
LVM.
# global_filter = []
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# The results of the filtering are cached on disk to avoid
# rescanning dud devices (which can take a very long time).
# By default this cache is stored in the /etc/lvm/cache directory
# in a file called '.cache'.
# It is safe to delete the contents: the tools regenerate it.
# (The old setting 'cache' is still respected if neither of
# these new ones is present.)
# N.B. If obtain_device_list_from_udev is set to 1 the list of
# devices is instead obtained from udev and any existing .cache
# file is removed.
cache_dir = "/etc/lvm/cache"
cache_file_prefix = ""
# You can turn off writing this cache file by setting this to 0.
write_cache_state = 1
# Advanced settings.
# List of pairs of additional acceptable block device types found
# in /proc/devices with maximum (non-zero) number of partitions.
# types = [ "fd", 16 ]
# If sysfs is mounted (2.6 kernels) restrict device scanning to
# the block devices it believes are valid.
# 1 enables; 0 disables.
sysfs_scan = 1
# By default, LVM2 will ignore devices used as component paths
# of device-mapper multipath devices.
# 1 enables; 0 disables.
multipath_component_detection = 1
# By default, LVM2 will ignore devices used as components of
# software RAID (md) devices by looking for md superblocks.
# 1 enables; 0 disables.
md_component_detection = 1
# By default, if a PV is placed directly upon an md device, LVM2
# will align its data blocks with the md device's stripe-width.
# 1 enables; 0 disables.
md_chunk_alignment = 1
# Default alignment of the start of a data area in MB. If set to 0,
# a value of 64KB will be used. Set to 1 for 1MiB, 2 for 2MiB, etc.
# default_data_alignment = 1
#
#
#
#
#
#
#
#
#
#
150
By default, the start of a PV's data area will be a multiple of
the 'minimum_io_size' or 'optimal_io_size' exposed in sysfs.
- minimum_io_size - the smallest request the device can perform
w/o incurring a read-modify-write penalty (e.g. MD's chunk size)
- optimal_io_size - the device's preferred unit of receiving I/O
(e.g. MD's stripe width)
minimum_io_size is used if optimal_io_size is undefined (0).
If md_chunk_alignment is enabled, that detects the optimal_io_size.
This setting takes precedence over md_chunk_alignment.
1 enables; 0 disables.
APPENDIX B. THE LVM CONFIGURATION FILES
data_alignment_detection = 1
# Alignment (in KB) of start of data area when creating a new PV.
# md_chunk_alignment and data_alignment_detection are disabled if set.
# Set to 0 for the default alignment (see: data_alignment_default)
# or page size, if larger.
data_alignment = 0
# By default, the start of the PV's aligned data area will be shifted
by
# the 'alignment_offset' exposed in sysfs. This offset is often 0 but
# may be non-zero; e.g.: certain 4KB sector drives that compensate for
# windows partitioning will have an alignment_offset of 3584 bytes
# (sector 7 is the lowest aligned logical block, the 4KB sectors start
# at LBA -1, and consequently sector 63 is aligned on a 4KB boundary).
# But note that pvcreate --dataalignmentoffset will skip this
detection.
# 1 enables; 0 disables.
data_alignment_offset_detection = 1
# If, while scanning the system for PVs, LVM2 encounters a devicemapper
# device that has its I/O suspended, it waits for it to become
accessible.
# Set this to 1 to skip such devices. This should only be needed
# in recovery situations.
ignore_suspended_devices = 0
# During each LVM operation errors received from each device are
counted.
# If the counter of a particular device exceeds the limit set here, no
# further I/O is sent to that device for the remainder of the
respective
# operation. Setting the parameter to 0 disables the counters
altogether.
disable_after_error_count = 0
# Allow use of pvcreate --uuid without requiring --restorefile.
require_restorefile_with_uuid = 1
# Minimum size (in KB) of block devices which can be used as PVs.
# In a clustered environment all nodes must use the same value.
# Any value smaller than 512KB is ignored.
# Ignore devices smaller than 2MB such as floppy drives.
pv_min_size = 2048
# The original built-in setting was 512 up to and including version
2.02.84.
# pv_min_size = 512
# Issue discards to a logical volumes's underlying physical volume(s)
when
# the logical volume is no longer using the physical volumes' space
(e.g.
# lvremove, lvreduce, etc). Discards inform the storage that a region
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is
# no longer in use. Storage that supports discards advertise the
protocol
# specific way discards should be issued by the kernel (TRIM, UNMAP,
or
# WRITE SAME with UNMAP bit set). Not all storage will support or
benefit
# from discards but SSDs and thinly provisioned LUNs generally do. If
set
# to 1, discards will only be issued if both the storage and kernel
provide
# support.
# 1 enables; 0 disables.
issue_discards = 0
}
# This section allows you to configure the way in which LVM selects
# free space for its Logical Volumes.
allocation {
#
#
#
#
#
#
#
When searching for free space to extend an LV, the "cling"
allocation policy will choose space on the same PVs as the last
segment of the existing LV. If there is insufficient space and a
list of tags is defined here, it will check whether any of them are
attached to the PVs concerned and then seek to match those PV tags
between existing extents and new extents.
Use the special tag "@*" as a wildcard to match any PV tag.
# Example: LVs are mirrored between two sites within a single VG.
# PVs are tagged with either @site1 or @site2 to indicate where
# they are situated.
# cling_tag_list = [ "@site1", "@site2" ]
# cling_tag_list = [ "@*" ]
# Changes made in version 2.02.85 extended the reach of the 'cling'
# policies to detect more situations where data can be grouped
# onto the same disks. Set this to 0 to revert to the previous
# algorithm.
maximise_cling = 1
# Set to 1 to guarantee that mirror logs will always be placed on
# different PVs from the mirror images. This was the default
# until version 2.02.85.
mirror_logs_require_separate_pvs = 0
# Set to 1 to guarantee that thin pool metadata will always
# be placed on different PVs from the pool data.
thin_pool_metadata_require_separate_pvs = 0
# Specify the minimal chunk size (in KB) for thin pool volumes.
# Use of the larger chunk size may improve perfomance for plain
# thin volumes, however using them for snapshot volumes is less
efficient,
# as it consumes more space and takes extra time for copying.
# When unset, lvm tries to estimate chunk size starting from 64KB
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APPENDIX B. THE LVM CONFIGURATION FILES
# Supported values are in range from 64 to 1048576.
# thin_pool_chunk_size = 64
# Specify discards behavior of the thin pool volume.
# Select one of "ignore", "nopassdown", "passdown"
# thin_pool_discards = "passdown"
#
#
#
#
Set to 0, to disable zeroing of thin pool data chunks before their
first use.
N.B. zeroing larger thin pool chunk size degrades performance.
thin_pool_zero = 1
}
# This section that allows you to configure the nature of the
# information that LVM2 reports.
log {
# Controls the messages sent to stdout or stderr.
# There are three levels of verbosity, 3 being the most verbose.
verbose = 0
# Set to 1 to suppress all non-essential messages from stdout.
# This has the same effect as -qq.
# When this is set, the following commands still produce output:
# dumpconfig, lvdisplay, lvmdiskscan, lvs, pvck, pvdisplay,
# pvs, version, vgcfgrestore -l, vgdisplay, vgs.
# Non-essential messages are shifted from log level 4 to log level 5
# for syslog and lvm2_log_fn purposes.
# Any 'yes' or 'no' questions not overridden by other arguments
# are suppressed and default to 'no'.
silent = 0
# Should we send log messages through syslog?
# 1 is yes; 0 is no.
syslog = 1
# Should we log error and debug messages to a file?
# By default there is no log file.
#file = "/var/log/lvm2.log"
# Should we overwrite the log file each time the program is run?
# By default we append.
overwrite = 0
# What level of log messages should we send to the log file and/or
syslog?
# There are 6 syslog-like log levels currently in use - 2 to 7
inclusive.
# 7 is the most verbose (LOG_DEBUG).
level = 0
# Format of output messages
# Whether or not (1 or 0) to indent messages according to their
severity
indent = 1
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# Whether or not (1 or 0) to display the command name on each line
output
command_names = 0
# A prefix to use before the message text (but after the command name,
# if selected). Default is two spaces, so you can see/grep the
severity
# of each message.
prefix = " "
# To make the messages look similar to the original LVM tools use:
#
indent = 0
#
command_names = 1
#
prefix = " -- "
# Set this if you want log messages during activation.
# Don't use this in low memory situations (can deadlock).
# activation = 0
# Some debugging messages are assigned to a class and only appear
# in debug output if the class is listed here.
# Classes currently available:
#
memory, devices, activation, allocation, lvmetad, metadata, cache,
#
locking
# Use "all" to see everything.
debug_classes = [ "memory", "devices", "activation", "allocation",
"lvmetad", "metadata", "cache", "locking" ]
}
# Configuration of metadata backups and archiving. In LVM2 when we
# talk about a 'backup' we mean making a copy of the metadata for the
# *current* system. The 'archive' contains old metadata configurations.
# Backups are stored in a human readeable text format.
backup {
# Should we maintain a backup of the current metadata configuration ?
# Use 1 for Yes; 0 for No.
# Think very hard before turning this off!
backup = 1
# Where shall we keep it ?
# Remember to back up this directory regularly!
backup_dir = "/etc/lvm/backup"
# Should we maintain an archive of old metadata configurations.
# Use 1 for Yes; 0 for No.
# On by default. Think very hard before turning this off.
archive = 1
# Where should archived files go ?
# Remember to back up this directory regularly!
archive_dir = "/etc/lvm/archive"
# What is the minimum number of archive files you wish to keep ?
retain_min = 10
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APPENDIX B. THE LVM CONFIGURATION FILES
# What is the minimum time you wish to keep an archive file for ?
retain_days = 30
}
# Settings for the running LVM2 in shell (readline) mode.
shell {
# Number of lines of history to store in ~/.lvm_history
history_size = 100
}
# Miscellaneous global LVM2 settings
global {
# The file creation mask for any files and directories created.
# Interpreted as octal if the first digit is zero.
umask = 077
# Allow other users to read the files
#umask = 022
# Enabling test mode means that no changes to the on disk metadata
# will be made. Equivalent to having the -t option on every
# command. Defaults to off.
test = 0
# Default value for --units argument
units = "h"
# Since version 2.02.54, the tools distinguish between powers of
# 1024 bytes (e.g. KiB, MiB, GiB) and powers of 1000 bytes (e.g.
# KB, MB, GB).
# If you have scripts that depend on the old behaviour, set this to 0
# temporarily until you update them.
si_unit_consistency = 1
# Whether or not to communicate with the kernel device-mapper.
# Set to 0 if you want to use the tools to manipulate LVM metadata
# without activating any logical volumes.
# If the device-mapper kernel driver is not present in your kernel
# setting this to 0 should suppress the error messages.
activation = 1
#
#
#
#
#
#
#
#
#
If we can't communicate with device-mapper, should we try running
the LVM1 tools?
This option only applies to 2.4 kernels and is provided to help you
switch between device-mapper kernels and LVM1 kernels.
The LVM1 tools need to be installed with .lvm1 suffices
e.g. vgscan.lvm1 and they will stop working after you start using
the new lvm2 on-disk metadata format.
The default value is set when the tools are built.
fallback_to_lvm1 = 0
# The default metadata format that commands should use - "lvm1" or
"lvm2".
# The command line override is -M1 or -M2.
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# Defaults to "lvm2".
# format = "lvm2"
# Location of proc filesystem
proc = "/proc"
# Type of locking to use. Defaults to local file-based locking (1).
# Turn locking off by setting to 0 (dangerous: risks metadata
corruption
# if LVM2 commands get run concurrently).
# Type 2 uses the external shared library locking_library.
# Type 3 uses built-in clustered locking.
# Type 4 uses read-only locking which forbids any operations that
might
# change metadata.
locking_type = 1
# Set to 0 to fail when a lock request cannot be satisfied
immediately.
wait_for_locks = 1
#
#
#
#
If using external locking (type 2) and initialisation fails,
with this set to 1 an attempt will be made to use the built-in
clustered locking.
If you are using a customised locking_library you should set this to
0.
fallback_to_clustered_locking = 1
# If an attempt to initialise type 2 or type 3 locking failed, perhaps
# because cluster components such as clvmd are not running, with this
set
# to 1 an attempt will be made to use local file-based locking (type
1).
# If this succeeds, only commands against local volume groups will
proceed.
# Volume Groups marked as clustered will be ignored.
fallback_to_local_locking = 1
# Local non-LV directory that holds file-based locks while commands
are
# in progress.
A directory like /tmp that may get wiped on reboot is
OK.
locking_dir = "/var/lock/lvm"
# Whenever there are competing read-only and read-write access
requests for
# a volume group's metadata, instead of always granting the read-only
# requests immediately, delay them to allow the read-write requests to
be
# serviced. Without this setting, write access may be stalled by a
high
# volume of read-only requests.
# NB. This option only affects locking_type = 1 viz. local file-based
# locking.
prioritise_write_locks = 1
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APPENDIX B. THE LVM CONFIGURATION FILES
# Other entries can go here to allow you to load shared libraries
# e.g. if support for LVM1 metadata was compiled as a shared library
use
#
format_libraries = "liblvm2format1.so"
# Full pathnames can be given.
# Search this directory first for shared libraries.
#
library_dir = "/lib"
# The external locking library to load if locking_type is set to 2.
#
locking_library = "liblvm2clusterlock.so"
# Treat any internal errors as fatal errors, aborting the process that
# encountered the internal error. Please only enable for debugging.
abort_on_internal_errors = 0
# Check whether CRC is matching when parsed VG is used multiple times.
# This is useful to catch unexpected internal cached volume group
# structure modification. Please only enable for debugging.
detect_internal_vg_cache_corruption = 0
# If set to 1, no operations that change on-disk metadata will be
permitted.
# Additionally, read-only commands that encounter metadata in need of
repair
# will still be allowed to proceed exactly as if the repair had been
# performed (except for the unchanged vg_seqno).
# Inappropriate use could mess up your system, so seek advice first!
metadata_read_only = 0
# 'mirror_segtype_default' defines which segtype will be used when the
# shorthand '-m' option is used for mirroring. The possible options
are:
#
# "mirror" - The original RAID1 implementation provided by LVM2/DM.
It is
#
characterized by a flexible log solution (core, disk,
mirrored)
#
and by the necessity to block I/O while reconfiguring in the
#
event of a failure.
#
#
There is an inherent race in the dmeventd failure handling
#
logic with snapshots of devices using this type of RAID1 that
#
in the worst case could cause a deadlock.
#
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=817130#c10
#
# "raid1" - This implementation leverages MD's RAID1 personality
through
#
device-mapper. It is characterized by a lack of log
options.
#
(A log is always allocated for every device and they are placed
#
on the same device as the image - no separate devices are
#
required.) This mirror implementation does not require I/O
#
to be blocked in the kernel in the event of a failure.
#
This mirror implementation is not cluster-aware and cannot be
#
used in a shared (active/active) fashion in a cluster.
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#
# Specify the '--type <mirror|raid1>' option to override this default
# setting.
mirror_segtype_default = "mirror"
# 'raid10_segtype_default' determines the segment types used by
default
# when the '--stripes/-i' and '--mirrors/-m' arguments are both
specified
# during the creation of a logical volume.
# Possible settings include:
#
# "raid10" - This implementation leverages MD's RAID10 personality
through
#
device-mapper.
#
# "mirror" - LVM will layer the 'mirror' and 'stripe' segment types.
It
#
will do this by creating a mirror on top of striped subLVs;
#
effectively creating a RAID 0+1 array. This is
suboptimal
#
in terms of providing redunancy and performance.
Changing to
#
this setting is not advised.
# Specify the '--type <raid10|mirror>' option to override this default
# setting.
raid10_segtype_default = "mirror"
# The default format for displaying LV names in lvdisplay was changed
# in version 2.02.89 to show the LV name and path separately.
# Previously this was always shown as /dev/vgname/lvname even when
that
# was never a valid path in the /dev filesystem.
# Set to 1 to reinstate the previous format.
#
# lvdisplay_shows_full_device_path = 0
# Whether to use (trust) a running instance of lvmetad. If this is set
to
# 0, all commands fall back to the usual scanning mechanisms. When set
to 1
# *and* when lvmetad is running (it is not auto-started), the volume
group
# metadata and PV state flags are obtained from the lvmetad instance
and no
# scanning is done by the individual commands. In a setup with
lvmetad,
# lvmetad udev rules *must* be set up for LVM to work correctly.
Without
# proper udev rules, all changes in block device configuration will be
# *ignored* until a manual 'pvscan --cache' is performed.
#
# If lvmetad has been running while use_lvmetad was 0, it MUST be
stopped
# before changing use_lvmetad to 1 and started again afterwards.
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APPENDIX B. THE LVM CONFIGURATION FILES
use_lvmetad = 0
# Full path of the utility called to check that a thin metadata device
# is in a state that allows it to be used.
# Each time a thin pool needs to be activated or after it is
deactivated
# this utility is executed. The activation will only proceed if the
utility
# has an exit status of 0.
# Set to "" to skip this check. (Not recommended.)
# The thin tools are available as part of the device-mapperpersistent-data
# package from https://github.com/jthornber/thin-provisioning-tools.
#
# thin_check_executable = "/usr/sbin/thin_check"
# Array of string options passed with thin_check command. By default,
# option "-q" is for quiet output.
# With thin_check version 2.1 or newer you can add "--ignore-nonfatal-errors"
# to let it pass through ignoreable errors and fix them later.
#
# thin_check_options = [ "-q" ]
#
#
#
#
#
#
Full path of the utility called to repair a thin metadata device
is in a state that allows it to be used.
Each time a thin pool needs repair this utility is executed.
See thin_check_executable how to obtain binaries.
thin_repair_executable = "/usr/sbin/thin_repair"
# Array of extra string options passed with thin_repair command.
# thin_repair_options = [ "" ]
# Full path of the utility called to dump thin metadata content.
# See thin_check_executable how to obtain binaries.
#
# thin_dump_executable = "/usr/sbin/thin_dump"
#
#
#
#
#
#
#
#
#
#
#
If set, given features are not used by thin driver.
This can be helpful not just for testing, but i.e. allows to avoid
using problematic implementation of some thin feature.
Features:
block_size
discards
discards_non_power_2
external_origin
metadata_resize
thin_disabled_features = [ "discards", "block_size" ]
}
activation {
# Set to 1 to perform internal checks on the operations issued to
# libdevmapper. Useful for debugging problems with activation.
# Some of the checks may be expensive, so it's best to use this
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# only when there seems to be a problem.
checks = 0
# Set to 0 to disable udev synchronisation (if compiled into the
binaries).
# Processes will not wait for notification from udev.
# They will continue irrespective of any possible udev processing
# in the background. You should only use this if udev is not running
# or has rules that ignore the devices LVM2 creates.
# The command line argument --nodevsync takes precedence over this
setting.
# If set to 1 when udev is not running, and there are LVM2 processes
# waiting for udev, run 'dmsetup udevcomplete_all' manually to wake
them up.
udev_sync = 1
# Set to 0 to disable the udev rules installed by LVM2 (if built with
# --enable-udev_rules). LVM2 will then manage the /dev nodes and
symlinks
# for active logical volumes directly itself.
# N.B. Manual intervention may be required if this setting is changed
# while any logical volumes are active.
udev_rules = 1
# Set to 1 for LVM2 to verify operations performed by udev. This turns
on
# additional checks (and if necessary, repairs) on entries in the
device
# directory after udev has completed processing its events.
# Useful for diagnosing problems with LVM2/udev interactions.
verify_udev_operations = 0
# If set to 1 and if deactivation of an LV fails, perhaps because
# a process run from a quick udev rule temporarily opened the device,
# retry the operation for a few seconds before failing.
retry_deactivation = 1
# How to fill in missing stripes if activating an incomplete volume.
# Using "error" will make inaccessible parts of the device return
# I/O errors on access. You can instead use a device path, in which
# case, that device will be used to in place of missing stripes.
# But note that using anything other than "error" with mirrored
# or snapshotted volumes is likely to result in data corruption.
missing_stripe_filler = "error"
# The linear target is an optimised version of the striped target
# that only handles a single stripe. Set this to 0 to disable this
# optimisation and always use the striped target.
use_linear_target = 1
# How much stack (in KB) to reserve for use while devices suspended
# Prior to version 2.02.89 this used to be set to 256KB
reserved_stack = 64
# How much memory (in KB) to reserve for use while devices suspended
reserved_memory = 8192
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APPENDIX B. THE LVM CONFIGURATION FILES
# Nice value used while devices suspended
process_priority = -18
#
#
#
#
#
#
or VG
#
#
#
#
#
#
#
#
#
#
#
If volume_list is defined, each LV is only activated if there is a
match against the list.
"vgname" and "vgname/lvname" are matched exactly.
"@tag" matches any tag set in the LV or VG.
"@*" matches if any tag defined on the host is also set in the LV
If any host tags exist but volume_list is not defined, a default
single-entry list containing "@*" is assumed.
volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]
If auto_activation_volume_list is defined, each LV that is to be
activated with the autoactivation option (--activate ay/-a ay) is
first checked against the list. There are two scenarios in which
the autoactivation option is used:
- automatic activation of volumes based on incoming PVs. If all
the
#
#
PVs making up a VG are present in the system, the autoactivation
is triggered. This requires lvmetad (global/use_lvmetad=1) and
udev
#
to be running. In this case, "pvscan --cache -aay" is called
#
automatically without any user intervention while processing
#
udev events. Please, make sure you define
auto_activation_volume_list
#
properly so only the volumes you want and expect are
autoactivated.
#
#
- direct activation on command line with the autoactivation
option.
#
In this case, the user calls "vgchange --activate ay/-a ay" or
#
"lvchange --activate ay/-a ay" directly.
#
# By default, the auto_activation_volume_list is not defined and all
# volumes will be activated either automatically or by using -activate ay/-a ay.
#
# N.B. The "activation/volume_list" is still honoured in all cases so
even
# if the VG/LV passes the auto_activation_volume_list, it still needs
to
# pass the volume_list for it to be activated in the end.
# If auto_activation_volume_list is defined but empty, no volumes will
be
# activated automatically and --activate ay/-a ay will do nothing.
#
# auto_activation_volume_list = []
# If auto_activation_volume_list is defined and it's not empty, only
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matching
# volumes will be activated either automatically or by using -activate ay/-a ay.
#
#
"vgname" and "vgname/lvname" are matched exactly.
#
"@tag" matches any tag set in the LV or VG.
#
"@*" matches if any tag defined on the host is also set in the LV
or VG
#
# auto_activation_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]
#
#
#
#
#
#
#
#
or VG
#
#
If read_only_volume_list is defined, each LV that is to be activated
is checked against the list, and if it matches, it as activated
in read-only mode. (This overrides '--permission rw' stored in the
metadata.)
"vgname" and "vgname/lvname" are matched exactly.
"@tag" matches any tag set in the LV or VG.
"@*" matches if any tag defined on the host is also set in the LV
read_only_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]
# Each LV can have an 'activation skip' flag stored persistently
against it.
# During activation, this flag is used to decide whether such an LV is
skipped.
# The 'activation skip' flag can be set during LV creation and by
default it
# is automatically set for thin snapshot LVs. The
'auto_set_activation_skip'
# enables or disables this automatic setting of the flag while LVs are
created.
# auto_set_activation_skip = 1
# For RAID or 'mirror' segment types, 'raid_region_size' is the
# size (in kiB) of each:
# - synchronization operation when initializing
# - each copy operation when performing a 'pvmove' (using 'mirror'
segtype)
# This setting has replaced 'mirror_region_size' since version 2.02.99
raid_region_size = 512
# Setting to use when there is no readahead value stored in the
metadata.
#
# "none" - Disable readahead.
# "auto" - Use default value chosen by kernel.
readahead = "auto"
# 'raid_fault_policy' defines how a device failure in a RAID logical
# volume is handled. This includes logical volumes that have the
following
# segment types: raid1, raid4, raid5*, and raid6*.
#
# In the event of a failure, the following policies will determine
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APPENDIX B. THE LVM CONFIGURATION FILES
what
# actions are performed during the automated response to failures
(when
# dmeventd is monitoring the RAID logical volume) and when 'lvconvert'
is
# called manually with the options '--repair' and '--use-policies'.
#
# "warn" - Use the system log to warn the user that a device in the
RAID
#
logical volume has failed. It is left to the user to run
#
'lvconvert --repair' manually to remove or replace the failed
#
device. As long as the number of failed devices does not
#
exceed the redundancy of the logical volume (1 device for
#
raid4/5, 2 for raid6, etc) the logical volume will remain
#
usable.
#
# "allocate" - Attempt to use any extra physical volumes in the volume
#
group as spares and replace faulty devices.
#
raid_fault_policy = "warn"
# 'mirror_image_fault_policy' and 'mirror_log_fault_policy' define
# how a device failure affecting a mirror (of "mirror" segment type)
is
# handled. A mirror is composed of mirror images (copies) and a log.
# A disk log ensures that a mirror does not need to be re-synced
# (all copies made the same) every time a machine reboots or crashes.
#
# In the event of a failure, the specified policy will be used to
determine
# what happens. This applies to automatic repairs (when the mirror is
being
# monitored by dmeventd) and to manual lvconvert --repair when
# --use-policies is given.
#
# "remove" - Simply remove the faulty device and run without it. If
#
the log device fails, the mirror would convert to using
#
an in-memory log. This means the mirror will not
#
remember its sync status across crashes/reboots and
#
the entire mirror will be re-synced. If a
#
mirror image fails, the mirror will convert to a
#
non-mirrored device if there is only one remaining good
#
copy.
#
# "allocate" - Remove the faulty device and try to allocate space on
#
a new device to be a replacement for the failed device.
#
Using this policy for the log is fast and maintains the
#
ability to remember sync state through crashes/reboots.
#
Using this policy for a mirror device is slow, as it
#
requires the mirror to resynchronize the devices, but it
#
will preserve the mirror characteristic of the device.
#
This policy acts like "remove" if no suitable device and
#
space can be allocated for the replacement.
#
# "allocate_anywhere" - Not yet implemented. Useful to place the log
device
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#
#
#
temporarily on same physical volume as one of the mirror
images. This policy is not recommended for mirror devices
since it would break the redundant nature of the mirror.
#
policy acts like "remove" if no suitable device and space
#
be allocated for the replacement.
This
can
mirror_log_fault_policy = "allocate"
mirror_image_fault_policy = "remove"
# 'snapshot_autoextend_threshold' and 'snapshot_autoextend_percent'
define
# how to handle automatic snapshot extension. The former defines when
the
# snapshot should be extended: when its space usage exceeds this many
# percent. The latter defines how much extra space should be allocated
for
# the snapshot, in percent of its current size.
#
# For example, if you set snapshot_autoextend_threshold to 70 and
# snapshot_autoextend_percent to 20, whenever a snapshot exceeds 70%
usage,
# it will be extended by another 20%. For a 1G snapshot, using up 700M
will
# trigger a resize to 1.2G. When the usage exceeds 840M, the snapshot
will
# be extended to 1.44G, and so on.
#
# Setting snapshot_autoextend_threshold to 100 disables automatic
# extensions. The minimum value is 50 (A setting below 50 will be
treated
# as 50).
snapshot_autoextend_threshold = 100
snapshot_autoextend_percent = 20
# 'thin_pool_autoextend_threshold' and 'thin_pool_autoextend_percent'
define
# how to handle automatic pool extension. The former defines when the
# pool should be extended: when its space usage exceeds this many
# percent. The latter defines how much extra space should be allocated
for
# the pool, in percent of its current size.
#
# For example, if you set thin_pool_autoextend_threshold to 70 and
# thin_pool_autoextend_percent to 20, whenever a pool exceeds 70%
usage,
# it will be extended by another 20%. For a 1G pool, using up 700M
will
# trigger a resize to 1.2G. When the usage exceeds 840M, the pool will
# be extended to 1.44G, and so on.
#
# Setting thin_pool_autoextend_threshold to 100 disables automatic
# extensions. The minimum value is 50 (A setting below 50 will be
treated
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APPENDIX B. THE LVM CONFIGURATION FILES
# as 50).
thin_pool_autoextend_threshold = 100
thin_pool_autoextend_percent = 20
# While activating devices, I/O to devices being (re)configured is
# suspended, and as a precaution against deadlocks, LVM2 needs to pin
# any memory it is using so it is not paged out. Groups of pages that
# are known not to be accessed during activation need not be pinned
# into memory. Each string listed in this setting is compared against
# each line in /proc/self/maps, and the pages corresponding to any
# lines that match are not pinned. On some systems locale-archive was
# found to make up over 80% of the memory used by the process.
# mlock_filter = [ "locale/locale-archive", "gconv/gconvmodules.cache" ]
# Set to 1 to revert to the default behaviour prior to version 2.02.62
# which used mlockall() to pin the whole process's memory while
activating
# devices.
use_mlockall = 0
# Monitoring is enabled by default when activating logical volumes.
# Set to 0 to disable monitoring or use the --ignoremonitoring option.
monitoring = 1
# When pvmove or lvconvert must wait for the kernel to finish
# synchronising or merging data, they check and report progress
# at intervals of this number of seconds. The default is 15 seconds.
# If this is set to 0 and there is only one thing to wait for, there
# are no progress reports, but the process is awoken immediately the
# operation is complete.
polling_interval = 15
}
####################
# Advanced section #
####################
# Metadata settings
#
# metadata {
# Default number of copies of metadata to hold on each PV. 0, 1 or 2.
# You might want to override it from the command line with 0
# when running pvcreate on new PVs which are to be added to large VGs.
# pvmetadatacopies = 1
#
#
#
#
#
#
#
Default number of copies of metadata to maintain for each VG.
If set to a non-zero value, LVM automatically chooses which of
the available metadata areas to use to achieve the requested
number of copies of the VG metadata. If you set a value larger
than the the total number of metadata areas available then
metadata is stored in them all.
The default value of 0 ("unmanaged") disables this automatic
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# management and allows you to control which metadata areas
# are used at the individual PV level using 'pvchange
# --metadataignore y/n'.
# vgmetadatacopies = 0
# Approximate default size of on-disk metadata areas in sectors.
# You should increase this if you have large volume groups or
# you want to retain a large on-disk history of your metadata changes.
# pvmetadatasize = 255
#
#
#
#
#
#
#
#
#
#
#
#
List of directories holding live copies of text format metadata.
These directories must not be on logical volumes!
It's possible to use LVM2 with a couple of directories here,
preferably on different (non-LV) filesystems, and with no other
on-disk metadata (pvmetadatacopies = 0). Or this can be in
addition to on-disk metadata areas.
The feature was originally added to simplify testing and is not
supported under low memory situations - the machine could lock up.
Never edit any files in these directories by hand unless you
you are absolutely sure you know what you are doing! Use
the supplied toolset to make changes (e.g. vgcfgrestore).
# dirs = [ "/etc/lvm/metadata", "/mnt/disk2/lvm/metadata2" ]
#}
# Event daemon
#
dmeventd {
# mirror_library is the library used when monitoring a mirror device.
#
# "libdevmapper-event-lvm2mirror.so" attempts to recover from
# failures. It removes failed devices from a volume group and
# reconfigures a mirror as necessary. If no mirror library is
# provided, mirrors are not monitored through dmeventd.
mirror_library = "libdevmapper-event-lvm2mirror.so"
# snapshot_library is the library used when monitoring a snapshot
device.
#
# "libdevmapper-event-lvm2snapshot.so" monitors the filling of
# snapshots and emits a warning through syslog when the use of
# the snapshot exceeds 80%. The warning is repeated when 85%, 90% and
# 95% of the snapshot is filled.
snapshot_library = "libdevmapper-event-lvm2snapshot.so"
#
#
#
#
#
#
166
thin_library is the library used when monitoring a thin device.
"libdevmapper-event-lvm2thin.so" monitors the filling of
pool and emits a warning through syslog when the use of
the pool exceeds 80%. The warning is repeated when 85%, 90% and
95% of the pool is filled.
APPENDIX B. THE LVM CONFIGURATION FILES
thin_library = "libdevmapper-event-lvm2thin.so"
# Full path of the dmeventd binary.
#
# executable = "/sbin/dmeventd"
}
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APPENDIX C. LVM SELECTION CRITERIA
As of Red Hat Enterpise Linux release 6.6, many LVM reporting commmands accept the -S or -select option to define selection criteria for those commands. As of Red Hat Enterprise Linux release
6.7, many processing commands support selection criteria as well. These two categories of commands
for which you can define selection criteria are defined as follows:
Reporting commands — Display only the lines that satisfy the selection criteria. Examples of
reporting commands for which you can define selection criteria include pvs, vgs, lvs,
pvdisplay, vgdisplay, lvdisplay, lvm devtypes, and dmsetup info -c.
Specifying the -o selected option in addition to the -S option displays all rows and adds a
"selected" column that shows 1 if the row matches the selection criteria and 0 if it does not.
Processing commands — Process only the items that satisfy the selection criteria. Examples of
processing commands for which you can define selection criteria include pvchange,
vgchange, lvchange, vgimport, vgexport, vgremove, and lvremove.
Selection criteria are a set of statements that use comparison operators to define the valid values for
particular fields to display or process. The selected fields are, in turn, combined by logical and grouping
operators.
When specifying which fields to display using selection criteria, there is no requirement for the field which
is in the selection criteria to be displayed. The selection criteria can contain one set of fields while the
output can contain a different set of fields.
For a listing of available fields for the various LVM components, see Section C.3, “Selection
Criteria Fields”.
For a listing of allowed operators, see Section C.2, “Selection Criteria Operators”. The operators
are also provided on the lvm(8) man page.
You can also see full sets of fields and possible operators by specifying the help (or ?) keyword
for the -S/--select option of a reporting commands. For example, the following command
displays the fields and possible operators for the lvs command.
# lvs -S help
For the Red Hat Enterprise Linux 6.8 release, you can specify time values as selection criteria for fields
with a field type of time. For information on specifying time values, see Section C.3.1, “Specifying Time
Values”.
C.1. SELECTION CRITERIA FIELD TYPES
The fields you specify for selection criteria are of a particular type. The help output for each field display
the field type enclosed in brackets. The following help output examples show the output indicating the
field types string, string_list, number, percent, and size.
lv_name
- Name. LVs created for internal use are enclosed in
brackets.[string]
lv_role
- LV role. [string list]
raid_mismatch_count - For RAID, number of mismatches found or repaired.
[number]
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APPENDIX C. LVM SELECTION CRITERIA
copy_percent
sync. [percent]
lv_size
- For RAID, mirrors and pvmove, current percentage in- Size of LV in current units. [size]
Table C.1, “Selection Criteria Field Types” describes the selection criteria field types
Table C.1. Selection Criteria Field Types
Field Type
Description
number
Non-negative integer value.
size
Floating point value with units, 'm' unit used by default if not specified.
percent
Non-negative integer with or without % suffix.
string
Characters quoted by ' or " or unquoted.
string list
Strings enclosed by [ ] or { } and elements delimited by either "all items must match" or
"at least one item must match" operator.
The values you specify for a field can be the following:
Concrete values of the field type
Regular expressions that include any fields of the string field type, such as "+~" operator.
Reserved values; for example -1, unknown, undefined, undef are all keywords to denote an
undefined numeric value.
Defined synonyms for the field values, which can be used in selection criteria for values just as
for their original values. For a listing of defined synonyms for field values, see Table C.14,
“Selection Criteria Synonyms”.
C.2. SELECTION CRITERIA OPERATORS
Table C.2, “Selection Criteria Grouping Operators” describes the selection criteria grouping operators.
Table C.2. Selection Criteria Grouping Operators
Grouping
Operator
Description
()
Used for grouping statements
[]
Used to group strings into a string list (exact match)
{}
Used to group strings into a string list (subset match)
Table C.3, “Selection Criteria Comparison Operators” describes the selection criteria comparison
operators and the field types with which they can be used.
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Table C.3. Selection Criteria Comparison Operators
Compar
ison
Operato
r
Description
Field Type
=~
Matching regular expression
regex
!~
Not matching regular expression.
regex
=
Equal to
number, size, percent, string, string list
!=
Not equal to
number, size, percent, string, string list
>=
Greater than or equal to
number, size, percent
>
Greater than
number, size, percent
<=
Less than or equal to
number, size, percent
<
Less than
number, size, percent
Table C.4, “Selection Criteria Logical and Grouping Operators” describes the selection criteria logical and
grouping operators.
Table C.4. Selection Criteria Logical and Grouping Operators
Logical and Grouping Operator
Description
&&
All fields must match
,
All fields must match (same as &&)
||
At least one field must match
#
At least one field must match (same as ||)
!
Logical negation
(
Left parenthesis (grouping operator)
)
Right parenthesis (grouping operator)
[
List start (grouping operator)
]
List end (grouping operator)
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APPENDIX C. LVM SELECTION CRITERIA
Logical and Grouping Operator
Description
{
List subset start (grouping operator)
}
List subset end (grouping operator)
C.3. SELECTION CRITERIA FIELDS
This section describes the logical and physical volume selection criteria fields you can specify.
Table C.5, “Logical Volume Fields” describes the logical volume fields and their field types.
Table C.5. Logical Volume Fields
Logical Volume Field
Description
Field Type
lv_uuid
Unique identifier
string
lv_name
Name (logical volumes created for internal use are
enclosed in brackets)
string
lv_full_name
Full name of logical volume including its volume
group, namely VG/LV
string
lv_path
Full pathname for logical volume (blank for internal
logical volumes)
string
lv_dm_path
Internal device mapper pathname for logical volume
(in /dev/mapper directory)
string
lv_parent
For logical volumes that are components of another
logical volume, the parent logical volume
string
lv_layout
logical volume layout
string list
lv_role
logical volume role
string list
lv_initial_image
_sync
Set if mirror/RAID images underwent initial
resynchronization
number
lv_image_synced
Set if mirror/RAID image is synchronized
number
lv_merging
Set if snapshot logical volume is being merged to
origin
number
lv_converting
Set if logical volume is being converted
number
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Logical Volume Manager Administration
Logical Volume Field
Description
Field Type
lv_allocation_po
licy
logical volume allocation policy
string
lv_allocation_lo
cked
Set if logical volume is locked against allocation
changes
number
lv_fixed_minor
Set if logical volume has fixed minor number
assigned
number
lv_merge_failed
Set if snapshot merge failed
number
lv_snapshot_inva
lid
Set if snapshot logical volume is invalid
number
lv_skip_activati
on
Set if logical volume is skipped on activation
number
lv_when_full
For thin pools, behavior when full
string
lv_active
Active state of the logical volume
string
lv_active_locall
y
Set if the logical volume is active locally
number
lv_active_remote
ly
Set if the logical volume is active remotely
number
lv_active_exclus
ively
Set if the logical volume is active exclusively
number
lv_major
Persistent major number or -1 if not persistent
number
lv_minor
Persistent minor number or -1 if not persistent
number
lv_read_ahead
Read ahead setting in current units
size
lv_size
Size of logical volume in current units
size
lv_metadata_size
For thin and cache pools, the size of the logical
volume that holds the metadata
size
seg_count
Number of segments in logical volume
number
origin
For snapshots, the origin device of this logical volume
string
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APPENDIX C. LVM SELECTION CRITERIA
Logical Volume Field
Description
Field Type
origin_size
For snapshots, the size of the origin device of this
logical volume
size
data_percent
For snapshot and thin pools and volumes, the
percentage full if logical volume is active
percent
snap_percent
For snapshots, the percentage full if logical volume is
active
percent
metadata_percent
For thin pools, the percentage of metadata full if
logical volume is active
percent
copy_percent
For RAID, mirrors and pvmove, current percentage
in-sync
percent
sync_percent
For RAID, mirrors and pvmove, current percentage
in-sync
percent
raid_mismatch_co
unt
For RAID, number of mismatches found or repaired
number
raid_sync_action
For RAID, the current synchronization action being
performed
string
raid_write_behin
d
For RAID1, the number of outstanding writes allowed
to writemostly devices
number
raid_min_recover
y_rate
For RAID1, the minimum recovery I/O load in
kiB/sec/disk
number
raid_max_recover
y_rate
For RAID1, the maximum recovery I/O load in
kiB/sec/disk
number
move_pv
For pvmove, source physical volume of temporary
logical volume created by pvmove
string
convert_lv
For lvconvert, name of temporary logical volume
created by lvconvert
string
mirror_log
For mirrors, the logical volume holding the
synchronization log
string
data_lv
For thin and cache pools, the logical volume holding
the associated data
string
metadata_lv
For thin and cache pools, the logical volume holding
the associated metadata
string
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Logical Volume Field
Description
Field Type
pool_lv
For thin volumes, the thin pool logical volume for this
volume
string
lv_tags
Tags, if any
string list
lv_profile
Configuration profile attached to this logical volume
string
lv_time
Creation time of the logical volume, if known
string
lv_host
Creation host of the logical volume, if known
string
lv_modules
Kernel device-mapper modules required for this
logical volume
string list
Table C.6, “Logical Volume Device Combined Info and Status Fields” describes the logical volume
device fields that combine both logical device info and logical device status.
Table C.6. Logical Volume Device Combined Info and Status Fields
Logical Volume Field
Description
Field Type
lv_attr
Selects according to both logical volume device info
as well as logical volume status.
string
Table C.7, “Logical Volume Device Info Fields” describes the logical volume device info fields and their
field types.
Table C.7. Logical Volume Device Info Fields
Logical Volume Field
Description
Field Type
lv_kernel_major
Currently assigned major number or -1 if logical
volume is not active
number
lv_kernel_minor
Currently assigned minor number or -1 if logical
volume is not active
number
lv_kernel_read_a
head
Currently-in-use read ahead setting in current units
size
lv_permissions
logical volume permissions
string
lv_suspended
Set if logical volume is suspended
number
lv_live_table
Set if logical volume has live table present
number
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APPENDIX C. LVM SELECTION CRITERIA
Logical Volume Field
Description
Field Type
lv_inactive_tabl
e
Set if logical volume has inactive table present
number
lv_device_open
Set if logical volume device is open
number
Table C.8, “Logical Volume Device Status Fields” describes the logical volume device status fields and
their field types.
Table C.8. Logical Volume Device Status Fields
Logical Volume Field
Description
Field Type
cache_total_bloc
ks
Total cache blocks
number
cache_used_block
s
Used cache blocks
number
cache_dirty_bloc
ks
Dirty cache blocks
number
cache_read_hits
Cache read hits
number
cache_read_misse
s
Cache read misses
number
cache_write_hits
Cache write hits
number
cache_write_miss
es
Cache write misses
number
lv_health_status
logical volume health status
string
Table C.9, “Physical Volume Label Fields” describes the physical volume label fields and their field types.
Table C.9. Physical Volume Label Fields
Physical Volume Field
Description
Field Type
pv_fmt
Type of metadata
string
pv_uuid
Unique identifier
string
dev_size
Size of underlying device in current units
size
pv_name
Name
string
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Physical Volume Field
Description
Field Type
pv_mda_free
Free metadata area space on this device in current
units
size
pv_mda_size
Size of smallest metadata area on this device in
current units
size
Table C.5, “Logical Volume Fields” describes the physical volume fields and their field types.
Table C.10. Pysical Volume Fields
Physical Volume Field
Description
Field Type
pe_start
Offset to the start of data on the underlying device
number
pv_size
Size of physical volume in current units
size
pv_free
Total amount of unallocated space in current units
size
pv_used
Total amount of allocated space in current units
size
pv_attr
Various attributes
string
pv_allocatable
Set if this device can be used for allocation
number
pv_exported
Set if this device is exported
number
pv_missing
Set if this device is missing in system
number
pv_pe_count
Total number of physical extents
number
pv_pe_alloc_coun
t
Total number of allocated physical extents
number
pv_tags
Tags, if any
string list
pv_mda_count
Number of metadata areas on this device
number
pv_mda_used_coun
t
Number of metadata areas in use on this device
number
pv_ba_start
Offset to the start of PV Bootloader Area on the
underlying device in current units
size
pv_ba_size
Size of PV Bootloader Area in current units
size
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Table C.11, “Volume Group Fields” describes the volume group fields and their field types.
Table C.11. Volume Group Fields
Volume Group Field
Description
Field Type
vg_fmt
Type of metadata
string
vg_uuid
Unique identifier
string
vg_name
Name
string
vg_attr
Various attributes
string
vg_permissions
Volume group permissions
string
vg_extendable
Set if volume group is extendable
number
vg_exported
Set if volume group is exported
number
vg_partial
Set if volume group is partial
number
vg_allocation_po
licy
Volume group allocation policy
string
vg_clustered
Set if volume group is clustered
number
vg_size
Total size of volume group in current units
size
vg_free
Total amount of free space in current units
size
vg_sysid
System ID of the volume group indicating which host
owns it
string
vg_systemid
System ID of the volume group indicating which host
owns it
string
vg_extent_size
Size of physical extents in current units
size
vg_extent_count
Total number of physical extents
number
vg_free_count
Total number of unallocated physical extents
number
max_lv
Maximum number of logical volumes allowed in
volume group or 0 if unlimited
number
max_pv
Maximum number of physical volumes allowed in
volume group or 0 if unlimited
number
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Volume Group Field
Description
Field Type
pv_count
Number of physical volumes
number
lv_count
Number of logical volumes
number
snap_count
Number of snapshots
number
vg_seqno
Revision number of internal metadata — incremented
whenever it changes
number
vg_tags
Tags, if any
string list
vg_profile
Configuration profile attached to this volume group
string
vg_mda_count
Number of metadata areas on this volume group
number
vg_mda_used_coun
t
Number of metadata areas in use on this volume
group
number
vg_mda_free
Free metadata area space for this volume group in
current units
size
vg_mda_size
Size of smallest metadata area for this volume group
in current units
size
vg_mda_copies
Target number of in use metadata areas in the
volume group
number
Table C.12, “Logical Volume Segment Fields” describes the logical volume segment fields and their field
types.
Table C.12. Logical Volume Segment Fields
Logical Volume
Segment Field
Description
Field Type
segtype
Type of logical volume segment
string
stripes
Number of stripes or mirror legs
number
stripesize
For stripes, amount of data placed on one device
before switching to the next
size
stripe_size
For stripes, amount of data placed on one device
before switching to the next
size
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APPENDIX C. LVM SELECTION CRITERIA
Logical Volume
Segment Field
Description
Field Type
regionsize
For mirrors, the unit of data copied when
synchronizing devices
size
region_size
For mirrors, the unit of data copied when
synchronizing devices
size
chunksize
For snapshots, the unit of data used when tracking
changes
size
chunk_size
For snapshots, the unit of data used when tracking
changes
size
thin_count
For thin pools, the number of thin volumes in this
pool
number
discards
For thin pools, how discards are handled
string
cachemode
For cache pools, how writes are cached
string
zero
For thin pools, if zeroing is enabled
number
transaction_id
For thin pools, the transaction id
number
thin_id
For thin volumes, the thin device id
number
seg_start
Offset within the logical volume to the start of the
segment in current units
size
seg_start_pe
Offset within the logical volume to the start of the
segment in physical extents.
number
seg_size
Size of segment in current units
size
seg_size_pe
Size of segment in physical extents
size
seg_tags
Tags, if any
string list
seg_pe_ranges
Ranges of physical extents of underlying devices in
command line format
string
devices
Underlying devices used with starting extent numbers
string
seg_monitor
dmeventd monitoring status of the segment
string
cache_policy
The cache policy (cached segments only)
string
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Logical Volume
Segment Field
Description
Field Type
cache_settings
Cache settings/parameters (cached segments only)
string list
Table C.13, “Pysical Volume Segment Fields” describes the physical volume segment fields and their
field types.
Table C.13. Pysical Volume Segment Fields
Physical Volume
Segment Field
Description
Field Type
pvseg_start
Physical extent number of start of segment
number
pvseg_size
Number of extents in segment
number
Table C.14, “Selection Criteria Synonyms” lists the synonyms you can use for field values. These
synonyms can be used in selection criteria as well as for values just like their original values. In this
table, a field value of "" indicates a blank string, which can be matched by specifying -S
'field_name=""'.
In this table, a field indicated by 0 or 1 indicates a binary value. You can specify a --binary option for
reporting tools which causes binary fields to display 0 or 1 instead of what is indicated in this table as
"some text" or "".
Table C.14. Selection Criteria Synonyms
Field
Field Value
Synonyms
pv_allocatable
allocatable
1
pv_allocatable
""
0
pv_exported
exported
1
pv_exported
""
0
pv_missing
missing
1
pv_missing
""
0
vg_extendable
extendable
1
vg_extendable
""
0
vg_exported
exported
1
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Field
Field Value
Synonyms
vg_exported
""
0
vg_partial
partial
1
vg_partial
""
0
vg_clustered
clustered
1
vg_clustered
""
0
vg_permissions
writeable
rw, read-write
vg_permissions
read-only
r, ro
vg_mda_copies
unmanaged
unknown, undefined, undef, -1
lv_initial_image_sync
initial image sync
sync, 1
lv_initial_image_sync
""
0
lv_image_synced
image synced
synced, 1
lv_image_synce
""
0
lv_merging
merging
1
lv_merging
""
0
lv_converting
converting
1
lv_converting
""
0
lv_allocation_locked
allocation locked
locked, 1
lv_allocation_locked
""
0
lv_fixed_minor
fixed minor
fixed, 1
lv_fixed_minor
""
0
lv_active_locally
active locally
active, locally, 1
lv_active_locally
""
0
lv_active_remotely
active remotely
active, remotely, 1
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Field
Field Value
Synonyms
lv_active_remotely
""
0
lv_active_exclusively
active exclusively
active, exclusively, 1
lv_active_exclusively
""
0
lv_merge_failed
merge failed
failed, 1
lv_merge_failed
""
0
lv_snapshot_invalid
snapshot invalid
invalid, 1
lv_snapshot_invalid
""
0
lv_suspended
suspended
1
lv_suspended
""
0
lv_live_table
live table present
live table, live, 1
lv_live_table
""
0
lv_inactive_table
inactive table present
inactive table, inactive, 1
lv_inactive_table
""
0
lv_device_open
open
1
lv_device_open
""
0
lv_skip_activation
skip activation
skip, 1
lv_skip_activation
""
0
zero
zero
1
zero
""
0
lv_permissions
writeable
rw, read-write
lv_permissions
read-only
r, ro
lv_permissions
read-only-override
ro-override, r-override, R
lv_when_full
error
error when full, error if no space
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APPENDIX C. LVM SELECTION CRITERIA
Field
Field Value
Synonyms
lv_when_full
queue
queue when full, queue if no
space
lv_when_full
""
undefined
cache_policy
""
undefined
seg_monitor
""
undefined
lv_health_status
""
undefined
C.3.1. Specifying Time Values
When specifying time values for LVM selection, you can use either a standardized time specification
format or a more free-form specification, as described in Section C.3.1.1, “Standard time selection
format” and Section C.3.1.2, “Freeform time selection format”.
You can specify the way time values are displayed with the report/time format configuration option in the
/etc/lvm/lvm.conf configuration file. Information on specifying this option is provided in the
lvm.conf file.
When specifying time values, you can use the comparison operator aliases since, after, until, and
before, as described in Table C.3, “Selection Criteria Comparison Operators”.
C.3.1.1. Standard time selection format
You can specify time values for LVM selection in the following format.
date time timezone
Table C.15, “Time Specification Formats” summarizes the formats you can use when specifying these
time values.
Table C.15. Time Specification Formats
Field
date
Field Value
YYYY-MM-DD
YYYY-MM, auto DD=1
YYYY, auto MM=01 and DD=01
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Field
Field Value
time
hh:mm:ss
hh:mm, auto ss=0
hh, auto mm=0, auto ss=0
timezone (always with +
or - sign)
+hh:mm or -hh:mm
+hh or -hh
The full date/time specification is YYYY-MM-DD hh:mm:ss. Users are able to leave date/time parts from
right to left. Whenever these parts are left out, a range is assumed automatically with second granularity.
For example:
"2015-07-07 9:51" means range of "2015-07-07 9:51:00" - "2015-07-07 9:51:59"
"2015-07" means range of "2015-07-01 0:00:00" - "2015-07-31 23:59:59"
"2015" means range of "2015-01-01 0:00:00" - "2015-12-31 23:59:59"
The following examples show the date/time specification as used in selection criteria.
lvs -S 'time since "2015-07-07 9:51"'
lvs -S 'time = "2015-07""
lvs -S 'time = "2015"'
C.3.1.2. Freeform time selection format
You can specify the date/time specification in LVM selection criteria using the following entitles.
weekday names ("Sunday" - "Saturday" or abbreviated as "Sun" - "Sat")
labels for points in time ("noon", "midnight")
labels for a day relative to current day ("today", "yesterday")
points back in time with relative offset from today (N is a number)
( "N" "seconds"/"minutes"/"hours"/"days"/"weeks"/"years" "ago")
( "N" "secs"/"mins"/"hrs" ... "ago")
( "N" "s"/"m"/"h" ... "ago")
time specification either in hh:mm:ss format or with AM/PM suffixes
month names ("January" - "December" or abbreviated as "Jan" - "Dec")
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APPENDIX C. LVM SELECTION CRITERIA
The following examples the show the freeform date/time specificaiton as used in selection criteria.
lvs
lvs
lvs
lvs
lvs
-S
-S
-S
-S
-S
'time
'time
'time
'time
'time
since "yesterday 9AM"'
since "Feb 3 years 2 months ago"'
= "February 2015"'
since "Jan 15 2015" && time until yesterday'
since "today 6AM"'
C.4. SELECTION CRITERIA DISPLAY EXAMPLES
This section provides a series of examples showing how to use selection criteria for LVM display
commands. The examples in this section use a system configured with LVM volumes that yield the
following output when selection criteria are not used.
# lvs -a -o+layout,role
LV
VG Attr
LSize
Pool Origin Data%
Role
root
f1 -wi-ao---9.01g
public
swap
f1 -wi-ao---- 512.00m
public
[lvol0_pmspare] vg ewi------4.00m
private,
\
pool,spare
lvol1
vg Vwi-a-tz-thin,sparse public
lvol2
vg Vwi-a-tz-thin,sparse public,
\
origin,
0.00
1.00g pool
0.00
Layout
linear
linear
linear
\
thinorigin
lvol3
vg Vwi---tz-k
thin,sparse public,
\
snapshot,
1.00g pool
Meta%
1.00g pool lvol2
\
thinsnapshot
pool
vg twi-aotz-- 100.00m
thin,pool
private
[pool_tdata]
vg Twi-ao---- 100.00m
private,
\
0.00
1.07
linear
thin,pool, \
data
[pool_tmeta]
private,
\
vg ewi-ao----
4.00m
linear
thin,pool, \
metadata
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The following command displays all logical volumes with "lvol[13]" in their name, using a regular
expression to specify this.
# lvs -a -o+layout,role -S 'lv_name=~lvol[13]'
LV
VG
Attr
LSize Pool Origin Data%
lvol1 vg
Vwi-a-tz-- 1.00g pool
0.00
lvol3 vg
Vwi---tz-k 1.00g pool lvol2
public,snapshot,thinsnapshot
Layout
Role
thin,sparse public
thin,sparse
The following command displays all logical volumes greater than 500m in size.
# lvs -a -o+layout,role -S 'lv_size>500m'
LV
VG Attr
LSize
Pool Origin Data%
root f1 -wi-ao---9.01g
swap f1 -wi-ao---- 512.00m
lvol1 vg Vwi-a-tz-1.00g pool
0.00
lvol2 vg Vwi-a-tz-1.00g pool
0.00
public,origin,thinorigin
lvol3 vg Vwi---tz-k
1.00g pool lvol2
public,snapshot,
\
Layout
linear
linear
thin,sparse
thin,sparse
Role
public
public
public
thin,sparse
thinsnapshot
The following command displays all logical volumes that include thin as a logical volume role, indicating
that the logical volume is used in constructing a thin pool. This example uses braces ({}) to indicate a
subset in the display.
# lvs -a -o+layout,role -S 'lv_role={thin}'
LV
VG
Attr
LSize
Layout
[pool_tdata] vg
Twi-ao---- 100.00m linear
[pool_tmeta] vg
ewi-ao---4.00m linear
private,thin,pool,metadata
Role
private,thin,pool,data
The following command displays all usable top-level logical volumes, which are the logical volumes with
a role of "public". If you do not specify braces ({}) in a string list to indicate a subset, it is assumed by
default; specifying lv_role=public is equivalent to specifying lv_role={public}.
# lvs -a -o+layout,role -S 'lv_role=public'
LV
VG Attr
LSize
Pool Origin Data%
root f1 -wi-ao---9.01g
swap f1 -wi-ao---- 512.00m
lvol1 vg Vwi-a-tz-1.00g pool
0.00
lvol2 vg Vwi-a-tz-1.00g pool
0.00
public,origin,thinorigin
lvol3 vg Vwi---tz-k
1.00g pool lvol2
public,snapshot,thinsnapshot
Layout
linear
linear
thin,sparse
thin,sparse
Role
public
public
public
thin,sparse
The following command displays all logical volumes with a thin layout.
# lvs -a -o+layout,role -S 'lv_layout={thin}'
LV
VG Attr
LSize
Pool Origin Data% Meta% Layout
Role
lvol1 vg Vwi-a-tz-1.00g pool
0.00
thin,sparse public
lvol2 vg Vwi-a-tz-1.00g pool
0.00
thin,sparse
public,origin,
\
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APPENDIX C. LVM SELECTION CRITERIA
thinorigin
lvol3 vg Vwi---tz-k
public,snapshot,
1.00g pool lvol2
\
thinsnapshot
pool vg twi-aotz-- 100.00m
thin,sparse
0.00
1.07
thin,pool
private
The following command displays all logical volumes with a layout field that matches "sparse,thin" exactly.
Note that it is not necessary to specify the string list members for the match to be positive.
# lvs -a -o+layout,role -S 'lv_layout=[sparse,thin]'
LV
VG
Attr
LSize Pool Origin Data% Layout
Role
lvol1 vg
Vwi-a-tz-- 1.00g pool
0.00
thin,sparse public
lvol2 vg
Vwi-a-tz-- 1.00g pool
0.00
thin,sparse
public,origin,thinorigin
lvol3 vg
Vwi---tz-k 1.00g pool lvol2
thin,sparse
public,snapshot,thinsnapshot
The following command displays the logical volume names of the logical volumes that are thin, sparse
logical volumes. Note that the list of fields used for selection criteria do not need to be the same as the list
of fields to display.
# lvs -a -o lv_name -S 'lv_layout=[sparse,thin]'
LV
lvol1
lvol2
lvol3
C.5. SELECTION CRITERIA PROCESSING EXAMPLES
This section provides a series of examples showing how to use selection criteria in commands that
process LVM logical volumes.
This example shows the initial configuration of a group of logical volumes, including thin snapshots. Thin
snapshots have the "skip activation" flag set by default. This example also includes the logical volume
lvol4 which also has the "skip activation" flag set.
# lvs -o name,skip_activation,layout,role
LV
SkipAct
Layout
Role
root
linear
public
swap
linear
public
lvol1
thin,sparse public
lvol2
thin,sparse public,origin,thinorigin
lvol3 skip activation thin,sparse public,snapshot,thinsnapshot
lvol4 skip activation linear
public
pool
thin,pool
private
The following command removes the skip activation flag from all logical volmes that are thin snapshots.
# lvchange --setactivationskip n -S 'role=thinsnapshot'
Logical volume "lvol3" changed.
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The following command shows the configuration of the logical volumes after executing the lvchange
command. Note that the "skip activation" flag has not been unset from the logical volume that is not a thin
snapshot.
# lvs -o name,active,skip_activation,layout,role
LV
Active SkipAct
Layout
Role
root active
linear
public
swap active
linear
public
lvol1 active
thin,sparse public
lvol2 active
thin,sparse public,origin,thinorigin
lvol3
thin,sparse public,snapshot,thinsnapshot
lvol4 active skip activation linear
public
pool active
thin,pool
private
The following command shows the configuration of the logical volumes after an additional thin
origin/snapshot volume has been created.
# lvs -o name,active,skip_activation,origin,layout,role
LV
Active SkipAct
Origin Layout
Role
root active
linear
public
swap active
linear
public
lvol1 active
thin,sparse public
lvol2 active
thin,sparse
public,origin,thinorigin
lvol3
lvol2 thin,sparse
public,snapshot,thinsnapshot
lvol4 active skip activation
linear
public
lvol5 active
thin,sparse
public,origin,thinorigin
lvol6
lvol5 thin,sparse
public,snapshot,thinsnapshot
pool active
thin,pool
private
The following command activates logical volumes that are both thin snapshot volumes and have an
origin volume of lvol2.
# lvchange -ay -S 'lv_role=thinsnapshot && origin=lvol2'
# lvs -o name,active,skip_activation,origin,layout,role
LV
Active SkipAct
Origin Layout
Role
root active
linear
public
swap active
linear
public
lvol1 active
thin,sparse public
lvol2 active
thin,sparse
public,origin,thinorigin
lvol3 active
lvol2 thin,sparse
public,snapshot,thinsnapshot
lvol4 active skip activation
linear
public
lvol5 active
thin,sparse
public,origin,thinorigin
lvol6
lvol5 thin,sparse
public,snapshot,thinsnapshot
pool active
thin,pool
private
If you execute a command on a whole item while specifying selection criteria that match an item from
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APPENDIX C. LVM SELECTION CRITERIA
that whole, the entire whole item is processed. For example, if you change a volume group while
selecting one or more items from that volume group, the whole volume group is selected. This example
selects logical volume lvol1, which is part of volume group vg. All of the logical volumes in volume
group vg are processed.
# lvs -o name,vg_name
LV
VG
root fedora
swap fedora
lvol1 vg
lvol2 vg
lvol3 vg
lvol4 vg
lvol5 vg
lvol6 vg
pool vg
# vgchange -ay -S 'lv_name=lvol1'
7 logical volume(s) in volume group "vg" now active
The following example shows a more complex selection criteria statement. In this example, all logical
volumes are tagged with "mytag" if they have a role of origin and are also named lvol[456] or the logical
volume size is more than 5g.
# lvchange --addtag mytag -S '(role=origin && lv_name=~lvol[456]) ||
lv_size > 5g'
Logical volume "root" changed.
Logical volume "lvol5" changed.
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APPENDIX D. LVM OBJECT TAGS
An LVM tag is a word that can be used to group LVM2 objects of the same type together. Tags can be
attached to objects such as physical volumes, volume groups, and logical volumes. Tags can be
attached to hosts in a cluster configuration.
Tags can be given on the command line in place of PV, VG or LV arguments. Tags should be prefixed
with @ to avoid ambiguity. Each tag is expanded by replacing it with all objects possessing that tag
which are of the type expected by its position on the command line.
As of the Red Hat Enterprise Linux 6.1 release, LVM tags are strings of up to 1024 characters (for earlier
releases the upper length limit was 128 characters). LVM tags cannot start with a hyphen.
A valid tag can consist of a limited range of characters only. For the Red Hat Enterprise Linux 6.0
release, the allowed characters are [A-Za-z0-9_+.-]. As of the Red Hat Enterprise Linux 6.1 release, the
list of allowed characters has been extended, and tags can contain the "/", "=", "!", ":", "#", and "&"
characters.
Only objects in a volume group can be tagged. Physical volumes lose their tags if they are removed from
a volume group; this is because tags are stored as part of the volume group metadata and that is deleted
when a physical volume is removed.
The following command lists all the logical volumes with the database tag.
lvs @database
The following command lists the currently active host tags.
lvm tags
D.1. ADDING AND REMOVING OBJECT TAGS
To add or delete tags from physical volumes, use the --addtag or --deltag option of the pvchange
command.
To add or delete tags from volume groups, use the --addtag or --deltag option of the vgchange or
vgcreate commands.
To add or delete tags from logical volumes, use the --addtag or --deltag option of the lvchange or
lvcreate commands.
As of the Red Hat Enterprise Linux 6.1 release, you can specify multiple --addtag and --deltag
arguments within a single pvchange, vgchange, or lvchange command. For example, the following
command deletes the tags T9 and T10 and adds the tags T13 and T14 to the volume group grant.
vgchange --deltag T9 --deltag T10 --addtag T13 --addtag T14 grant
D.2. HOST TAGS
In a cluster configuration, you can define host tags in the configuration files. If you set hosttags = 1 in
the tags section, a host tag is automatically defined using the machine's host name. This allow you to
use a common configuration file which can be replicated on all your machines so they hold identical
copies of the file, but the behavior can differ between machines according to the host name.
190
APPENDIX D. LVM OBJECT TAGS
For information on the configuration files, see Appendix B, The LVM Configuration Files.
For each host tag, an extra configuration file is read if it exists: lvm_hosttag.conf. If that file defines new
tags, then further configuration files will be appended to the list of files to read in.
For example, the following entry in the configuration file always defines tag1, and defines tag2 if the
host name is host1.
tags { tag1 { }
tag2 { host_list = ["host1"] } }
D.3. CONTROLLING ACTIVATION WITH TAGS
You can specify in the configuration file that only certain logical volumes should be activated on that host.
For example, the following entry acts as a filter for activation requests (such as vgchange -ay) and
only activates vg1/lvol0 and any logical volumes or volume groups with the database tag in the
metadata on that host.
activation { volume_list = ["vg1/lvol0", "@database" ] }
There is a special match "@*" that causes a match only if any metadata tag matches any host tag on
that machine.
As another example, consider a situation where every machine in the cluster has the following entry in
the configuration file:
tags { hosttags = 1 }
If you want to activate vg1/lvol2 only on host db2, do the following:
1. Run lvchange --addtag @db2 vg1/lvol2 from any host in the cluster.
2. Run lvchange -ay vg1/lvol2.
This solution involves storing hostnames inside the volume group metadata.
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Logical Volume Manager Administration
APPENDIX E. LVM VOLUME GROUP METADATA
The configuration details of a volume group are referred to as the metadata. By default, an identical copy
of the metadata is maintained in every metadata area in every physical volume within the volume group.
LVM volume group metadata is stored as ASCII.
If a volume group contains many physical volumes, having many redundant copies of the metadata is
inefficient. It is possible to create a physical volume without any metadata copies by using the -metadatacopies 0 option of the pvcreate command. Once you have selected the number of
metadata copies the physical volume will contain, you cannot change that at a later point. Selecting 0
copies can result in faster updates on configuration changes. Note, however, that at all times every
volume group must contain at least one physical volume with a metadata area (unless you are using the
advanced configuration settings that allow you to store volume group metadata in a file system). If you
intend to split the volume group in the future, every volume group needs at least one metadata copy.
The core metadata is stored in ASCII. A metadata area is a circular buffer. New metadata is appended to
the old metadata and then the pointer to the start of it is updated.
You can specify the size of metadata area with the --metadatasize. option of the pvcreate
command. The default size may be too small for volume groups that contain physical volumes and
logical volumes that number in the hundreds.
E.1. THE PHYSICAL VOLUME LABEL
By default, the pvcreate command places the physical volume label in the 2nd 512-byte sector. This
label can optionally be placed in any of the first four sectors, since the LVM tools that scan for a physical
volume label check the first 4 sectors. The physical volume label begins with the string LABELONE.
The physical volume label Contains:
Physical volume UUID
Size of block device in bytes
NULL-terminated list of data area locations
NULL-terminated lists of metadata area locations
Metadata locations are stored as offset and size (in bytes). There is room in the label for about 15
locations, but the LVM tools currently use 3: a single data area plus up to two metadata areas.
E.2. METADATA CONTENTS
The volume group metadata contains:
Information about how and when it was created
Information about the volume group:
The volume group information contains:
Name and unique id
A version number which is incremented whenever the metadata gets updated
192
APPENDIX E. LVM VOLUME GROUP METADATA
Any properties: Read/Write? Resizeable?
Any administrative limit on the number of physical volumes and logical volumes it may contain
The extent size (in units of sectors which are defined as 512 bytes)
An unordered list of physical volumes making up the volume group, each with:
Its UUID, used to determine the block device containing it
Any properties, such as whether the physical volume is allocatable
The offset to the start of the first extent within the physical volume (in sectors)
The number of extents
An unordered list of logical volumes. each consisting of
An ordered list of logical volume segments. For each segment the metadata includes a
mapping applied to an ordered list of physical volume segments or logical volume segments
E.3. SAMPLE METADATA
The following shows an example of LVM volume group metadata for a volume group called myvg.
# Generated by LVM2: Tue Jan 30 16:28:15 2007
contents = "Text Format Volume Group"
version = 1
description = "Created *before* executing 'lvextend -L+5G /dev/myvg/mylv
/dev/sdc'"
creation_host = "tng3-1"
26 14:15:21 EST 2007 i686
creation_time = 1170196095
# Linux tng3-1 2.6.18-8.el5 #1 SMP Fri Jan
# Tue Jan 30 16:28:15 2007
myvg {
id = "0zd3UT-wbYT-lDHq-lMPs-EjoE-0o18-wL28X4"
seqno = 3
status = ["RESIZEABLE", "READ", "WRITE"]
extent_size = 8192
# 4 Megabytes
max_lv = 0
max_pv = 0
physical_volumes {
pv0 {
id = "ZBW5qW-dXF2-0bGw-ZCad-2RlV-phwu-1c1RFt"
device = "/dev/sda"
# Hint only
status =
dev_size
pe_start
pe_count
["ALLOCATABLE"]
= 35964301
# 17.1491 Gigabytes
= 384
= 4390 # 17.1484 Gigabytes
}
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Logical Volume Manager Administration
pv1 {
id = "ZHEZJW-MR64-D3QM-Rv7V-Hxsa-zU24-wztY19"
device = "/dev/sdb"
# Hint only
status =
dev_size
pe_start
pe_count
["ALLOCATABLE"]
= 35964301
# 17.1491 Gigabytes
= 384
= 4390 # 17.1484 Gigabytes
}
pv2 {
id = "wCoG4p-55Ui-9tbp-VTEA-jO6s-RAVx-UREW0G"
device = "/dev/sdc"
# Hint only
status =
dev_size
pe_start
pe_count
["ALLOCATABLE"]
= 35964301
# 17.1491 Gigabytes
= 384
= 4390 # 17.1484 Gigabytes
}
pv3 {
id = "hGlUwi-zsBg-39FF-do88-pHxY-8XA2-9WKIiA"
device = "/dev/sdd"
# Hint only
status =
dev_size
pe_start
pe_count
["ALLOCATABLE"]
= 35964301
# 17.1491 Gigabytes
= 384
= 4390 # 17.1484 Gigabytes
}
}
logical_volumes {
mylv {
id = "GhUYSF-qVM3-rzQo-a6D2-o0aV-LQet-Ur9OF9"
status = ["READ", "WRITE", "VISIBLE"]
segment_count = 2
segment1 {
start_extent = 0
extent_count = 1280
type = "striped"
stripe_count = 1
# 5 Gigabytes
# linear
stripes = [
"pv0", 0
]
}
segment2 {
start_extent = 1280
extent_count = 1280
type = "striped"
stripe_count = 1
194
# 5 Gigabytes
# linear
APPENDIX E. LVM VOLUME GROUP METADATA
stripes = [
"pv1", 0
]
}
}
}
}
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Logical Volume Manager Administration
APPENDIX F. REVISION HISTORY
Revision 10.0-3
Wed Mar 8 2017
Steven Levine
Fri Dec 16 2016
Steven Levine
Tue Nov 29 2016
Steven Levine
Wed Apr 27 2016
Steven Levine
Version for 6.9 GA Publication
Revision 10.0-1
Version for 6.9 Beta Publication
Revision 9.0-5
Updating document for 6.8.
Revision 9.0-4
Preparing document for 6.8 GA publication.
Revision 9.0-3
Wed Mar 9 2016
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.8 Beta release
Revision 8.0-16
Mon Jul 13 2015
Steven Levine
Republish version for Red Hat Enterprise Linux 6.7
Revision 8.0-14
Wed Jul 8 2015
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.7
Revision 8.0-13
Tue Apr 14 2015
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.7 Beta release
Revision 7.0-9
Wed Oct 8 2014
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.6
Revision 7.0-8
Thu Aug 7 2014
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.6 Beta release
Revision 6.0-14
Wed Nov 13 2013
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.5
Revision 6.0-10
Fri Sep 27 2013
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.5 Beta release
Revision 5.0-19
Mon Feb 18 2013
John Ha
Initial revision for Red Hat Enterprise Linux 6.4
Revision 5.0-12
Mon Nov 27 2012
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.4 Beta release
Revision 4.0-2
Fri Jun 15 2012
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.3
Revision 3.0-1
Mon Sep 19 2011
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.2 Beta release
Revision 2.0-1
Thu May 19 2011
Steven Levine
Initial revision for Red Hat Enterprise Linux 6.1
Revision 1.0-1
Wed Nov 10 2010
Initial release for Red Hat Enterprise Linux 6
196
Steven Levine
INDEX
INDEX
Symbols
/lib/udev/rules.d directory, udev Integration with the Device Mapper
A
activating logical volumes
individual nodes, Activating Logical Volumes on Individual Nodes in a Cluster
activating volume groups, Activating and Deactivating Volume Groups
individual nodes, Activating and Deactivating Volume Groups
local node only, Activating and Deactivating Volume Groups
administrative procedures, LVM Administration Overview
allocation, LVM Allocation
policy, Creating Volume Groups
preventing, Preventing Allocation on a Physical Volume
archive file, Logical Volume Backup, Backing Up Volume Group Metadata
B
backup
file, Logical Volume Backup
metadata, Logical Volume Backup, Backing Up Volume Group Metadata
backup file, Backing Up Volume Group Metadata
block device
scanning, Scanning for Block Devices
C
cache file
building, Scanning Disks for Volume Groups to Build the Cache File
cache logical volume
creation, Creating LVM Cache Logical Volumes
cache volumes, Cache Volumes
cluster environment, The Clustered Logical Volume Manager (CLVM), Creating LVM Volumes in a
Cluster
CLVM
definition, The Clustered Logical Volume Manager (CLVM)
clvmd daemon, The Clustered Logical Volume Manager (CLVM)
command line units, Using CLI Commands
197
Logical Volume Manager Administration
configuration examples, LVM Configuration Examples
creating
logical volume, Creating Linear Logical Volumes
logical volume, example, Creating an LVM Logical Volume on Three Disks
LVM volumes in a cluster, Creating LVM Volumes in a Cluster
physical volumes, Creating Physical Volumes
striped logical volume, example, Creating a Striped Logical Volume
volume group, clustered, Creating Volume Groups in a Cluster
volume groups, Creating Volume Groups
creating LVM volumes
overview, Logical Volume Creation Overview
D
data relocation, online, Online Data Relocation
deactivating volume groups, Activating and Deactivating Volume Groups
exclusive on one node, Activating and Deactivating Volume Groups
local node only, Activating and Deactivating Volume Groups
device numbers
major, Persistent Device Numbers
minor, Persistent Device Numbers
persistent, Persistent Device Numbers
device path names, Using CLI Commands
device scan filters, Controlling LVM Device Scans with Filters
device size, maximum, Creating Volume Groups
device special file directory, Creating Volume Groups
display
sorting output, Sorting LVM Reports
displaying
logical volumes, Displaying Logical Volumes, The lvs Command
physical volumes, Displaying Physical Volumes, The pvs Command
volume groups, Displaying Volume Groups, The vgs Command
E
extent
allocation, Creating Volume Groups, LVM Allocation
definition, Volume Groups, Creating Volume Groups
F
198
INDEX
failed devices
displaying, Displaying Information on Failed Devices
features, new and changed, New and Changed Features
feedback
contact information for this manual, We Need Feedback!
file system
growing on a logical volume, Growing a File System on a Logical Volume
filters, Controlling LVM Device Scans with Filters
G
growing file system
logical volume, Growing a File System on a Logical Volume
H
help display, Using CLI Commands
I
initializing
partitions, Initializing Physical Volumes
physical volumes, Initializing Physical Volumes
Insufficient Free Extents message, Insufficient Free Extents for a Logical Volume
L
linear logical volume
converting to mirrored, Changing Mirrored Volume Configuration
creation, Creating Linear Logical Volumes
definition, Linear Volumes
logging, Logging
logical volume
activation, Controlling Logical Volume Activation
administration, general, Logical Volume Administration
cache, Creating LVM Cache Logical Volumes
changing parameters, Changing the Parameters of a Logical Volume Group
creation, Creating Linear Logical Volumes
creation example, Creating an LVM Logical Volume on Three Disks
definition, Logical Volumes, LVM Logical Volumes
displaying, Displaying Logical Volumes, Customized Reporting for LVM, The lvs Command
exclusive access, Activating Logical Volumes on Individual Nodes in a Cluster
extending, Growing Logical Volumes
199
Logical Volume Manager Administration
growing, Growing Logical Volumes
linear, Creating Linear Logical Volumes
local access, Activating Logical Volumes on Individual Nodes in a Cluster
lvs display arguments, The lvs Command
mirrored, Creating Mirrored Volumes
reducing, Shrinking Logical Volumes
removing, Removing Logical Volumes
renaming, Renaming Logical Volumes
shrinking, Shrinking Logical Volumes
snapshot, Creating Snapshot Volumes
striped, Creating Striped Volumes
thinly-provisioned, Creating Thinly-Provisioned Logical Volumes
thinly-provisioned snapshot, Creating Thinly-Provisioned Snapshot Volumes
lvchange command, Changing the Parameters of a Logical Volume Group
lvconvert command, Changing Mirrored Volume Configuration
lvcreate command, Creating Linear Logical Volumes
lvdisplay command, Displaying Logical Volumes
lvextend command, Growing Logical Volumes
LVM
architecture overview, LVM Architecture Overview
clustered, The Clustered Logical Volume Manager (CLVM)
components, LVM Architecture Overview, LVM Components
custom report format, Customized Reporting for LVM
directory structure, Creating Volume Groups
help, Using CLI Commands
history, LVM Architecture Overview
label, Physical Volumes
logging, Logging
logical volume administration, Logical Volume Administration
physical volume administration, Physical Volume Administration
physical volume, definition, Physical Volumes
volume group, definition, Volume Groups
LVM1, LVM Architecture Overview
LVM2, LVM Architecture Overview
lvmdiskscan command, Scanning for Block Devices
lvmetad daemon, The Metadata Daemon (lvmetad)
lvreduce command, Shrinking Logical Volumes
lvremove command, Removing Logical Volumes
lvrename command, Renaming Logical Volumes
lvs command, Customized Reporting for LVM, The lvs Command
200
INDEX
display arguments, The lvs Command
lvscan command, Displaying Logical Volumes
M
man page display, Using CLI Commands
metadata
backup, Logical Volume Backup, Backing Up Volume Group Metadata
recovery, Recovering Physical Volume Metadata
metadata daemon, The Metadata Daemon (lvmetad)
mirrored logical volume
clustered, Creating a Mirrored LVM Logical Volume in a Cluster
converting to linear, Changing Mirrored Volume Configuration
creation, Creating Mirrored Volumes
definition, Mirrored Logical Volumes
extending, Extending a Mirrored Volume
failure policy, Mirrored Logical Volume Failure Policy
failure recovery, Recovering from LVM Mirror Failure
growing, Extending a Mirrored Volume
reconfiguration, Changing Mirrored Volume Configuration
mirror_image_fault_policy configuration parameter, Mirrored Logical Volume Failure Policy
mirror_log_fault_policy configuration parameter, Mirrored Logical Volume Failure Policy
O
online data relocation, Online Data Relocation
overview
features, new and changed, New and Changed Features
P
partition type, setting, Setting the Partition Type
partitions
multiple, Multiple Partitions on a Disk
path names, Using CLI Commands
persistent device numbers, Persistent Device Numbers
physical extent
preventing allocation, Preventing Allocation on a Physical Volume
physical volume
adding to a volume group, Adding Physical Volumes to a Volume Group
administration, general, Physical Volume Administration
creating, Creating Physical Volumes
201
Logical Volume Manager Administration
definition, Physical Volumes
display, The pvs Command
displaying, Displaying Physical Volumes, Customized Reporting for LVM
illustration, LVM Physical Volume Layout
initializing, Initializing Physical Volumes
layout, LVM Physical Volume Layout
pvs display arguments, The pvs Command
recovery, Replacing a Missing Physical Volume
removing, Removing Physical Volumes
removing from volume group, Removing Physical Volumes from a Volume Group
removing lost volume, Removing Lost Physical Volumes from a Volume Group
resizing, Resizing a Physical Volume
pvdisplay command, Displaying Physical Volumes
pvmove command, Online Data Relocation
pvremove command, Removing Physical Volumes
pvresize command, Resizing a Physical Volume
pvs command, Customized Reporting for LVM
display arguments, The pvs Command
pvscan command, Displaying Physical Volumes
R
RAID logical volume, RAID Logical Volumes
removing
disk from a logical volume, Removing a Disk from a Logical Volume
logical volume, Removing Logical Volumes
physical volumes, Removing Physical Volumes
renaming
logical volume, Renaming Logical Volumes
volume group, Renaming a Volume Group
report format, LVM devices, Customized Reporting for LVM
resizing
physical volume, Resizing a Physical Volume
rules.d directory, udev Integration with the Device Mapper
S
scanning
block devices, Scanning for Block Devices
scanning devices, filters, Controlling LVM Device Scans with Filters
202
INDEX
snapshot logical volume
creation, Creating Snapshot Volumes
snapshot volume
definition, Snapshot Volumes
striped logical volume
creation, Creating Striped Volumes
creation example, Creating a Striped Logical Volume
definition, Striped Logical Volumes
extending, Extending a Striped Volume
growing, Extending a Striped Volume
T
thin snapshot volume, Thinly-Provisioned Snapshot Volumes
thin volume
creation, Creating Thinly-Provisioned Logical Volumes
thinly-provisioned logical volume, Thinly-Provisioned Logical Volumes (Thin Volumes)
creation, Creating Thinly-Provisioned Logical Volumes
thinly-provisioned snapshot logical volume
creation, Creating Thinly-Provisioned Snapshot Volumes
thinly-provisioned snapshot volume, Thinly-Provisioned Snapshot Volumes
troubleshooting, LVM Troubleshooting
U
udev device manager, Device Mapper Support for the udev Device Manager
udev rules, udev Integration with the Device Mapper
units, command line, Using CLI Commands
V
verbose output, Using CLI Commands
vgcfbackup command, Backing Up Volume Group Metadata
vgcfrestore command, Backing Up Volume Group Metadata
vgchange command, Changing the Parameters of a Volume Group
vgcreate command, Creating Volume Groups, Creating Volume Groups in a Cluster
vgdisplay command, Displaying Volume Groups
vgexport command, Moving a Volume Group to Another System
vgextend command, Adding Physical Volumes to a Volume Group
vgimport command, Moving a Volume Group to Another System
vgmerge command, Combining Volume Groups
vgmknodes command, Recreating a Volume Group Directory
203
Logical Volume Manager Administration
vgreduce command, Removing Physical Volumes from a Volume Group
vgrename command, Renaming a Volume Group
vgs command, Customized Reporting for LVM
display arguments, The vgs Command
vgscan command, Scanning Disks for Volume Groups to Build the Cache File
vgsplit command, Splitting a Volume Group
volume group
activating, Activating and Deactivating Volume Groups
administration, general, Volume Group Administration
changing parameters, Changing the Parameters of a Volume Group
combining, Combining Volume Groups
creating, Creating Volume Groups
creating in a cluster, Creating Volume Groups in a Cluster
deactivating, Activating and Deactivating Volume Groups
definition, Volume Groups
displaying, Displaying Volume Groups, Customized Reporting for LVM, The vgs Command
extending, Adding Physical Volumes to a Volume Group
growing, Adding Physical Volumes to a Volume Group
merging, Combining Volume Groups
moving between systems, Moving a Volume Group to Another System
reducing, Removing Physical Volumes from a Volume Group
removing, Removing Volume Groups
renaming, Renaming a Volume Group
shrinking, Removing Physical Volumes from a Volume Group
splitting, Splitting a Volume Group
example procedure, Splitting a Volume Group
vgs display arguments, The vgs Command
204
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