Red Hat Enterprise Linux 6 Logical Volume Manager Administrator guide

Red Hat Enterprise Linux 6

Logical Volume

Manager Administration

LVM Administrator Guide

Logical Volume Manager Administration

Red Hat Enterprise Linux 6 Logical Volume Manager

Administration

LVM Administrator Guide

Edition 1

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This book describes the LVM logical volume manager, including information on running LVM in a clustered environment.

Introduction vii

1. About This Guide .......................................................................................................... vii

2. Audience ....................................................................................................................... vii

3. Software Versions .......................................................................................................... vii

4. Related Documentation .................................................................................................. vii

5. We Need Feedback! ..................................................................................................... viii

6. Document Conventions ................................................................................................. viii

6.1. Typographic Conventions .................................................................................... viii

6.2. Pull-quote Conventions ......................................................................................... x

6.3. Notes and Warnings ............................................................................................. x

1. The LVM Logical Volume Manager 1

1.1. New and Changed Features ......................................................................................... 1

1.1.1. New and Changed Features for Red Hat Enterprise Linux 6.0 .............................. 1

1.1.2. New and Changed Features for Red Hat Enterprise Linux 6.1 .............................. 2

1.1.3. New and Changed Features for Red Hat Enterprise Linux 6.2 .............................. 2

1.2. Logical Volumes ........................................................................................................... 2

1.3. LVM Architecture Overview ........................................................................................... 3

1.4. The Clustered Logical Volume Manager (CLVM) ............................................................ 4

1.5. Document Overview ..................................................................................................... 6

2. LVM Components 9

2.1. Physical Volumes ......................................................................................................... 9

2.1.1. LVM Physical Volume Layout ............................................................................. 9

2.1.2. Multiple Partitions on a Disk ............................................................................. 10

2.2. Volume Groups .......................................................................................................... 10

2.3. LVM Logical Volumes ................................................................................................. 11

2.3.1. Linear Volumes ................................................................................................ 11

2.3.2. Striped Logical Volumes ................................................................................... 12

2.3.3. Mirrored Logical Volumes ................................................................................. 13

2.3.4. Snapshot Volumes ........................................................................................... 14

3. LVM Administration Overview 17

3.1. Creating LVM Volumes in a Cluster ............................................................................. 17

3.2. Logical Volume Creation Overview .............................................................................. 17

3.3. Growing a File System on a Logical Volume ................................................................ 18

3.4. Logical Volume Backup .............................................................................................. 18

3.5. Logging ...................................................................................................................... 19

4. LVM Administration with CLI Commands 21

4.1. Using CLI Commands ................................................................................................ 21

4.2. Physical Volume Administration ................................................................................... 22

4.2.1. Creating Physical Volumes ............................................................................... 22

4.2.2. Displaying Physical Volumes ............................................................................ 24

4.2.3. Preventing Allocation on a Physical Volume ...................................................... 25

4.2.4. Resizing a Physical Volume ............................................................................. 25

4.2.5. Removing Physical Volumes ............................................................................ 25

4.3. Volume Group Administration ...................................................................................... 25

4.3.1. Creating Volume Groups .................................................................................. 25

4.3.2. Creating Volume Groups in a Cluster ................................................................ 26

4.3.3. Adding Physical Volumes to a Volume Group .................................................... 27

4.3.4. Displaying Volume Groups ............................................................................... 27

4.3.5. Scanning Disks for Volume Groups to Build the Cache File ................................ 28

4.3.6. Removing Physical Volumes from a Volume Group ............................................ 29

4.3.7. Changing the Parameters of a Volume Group .................................................... 29

4.3.8. Activating and Deactivating Volume Groups ...................................................... 30

iii

Logical Volume Manager Administration

4.3.9. Removing Volume Groups ................................................................................ 30

4.3.10. Splitting a Volume Group ............................................................................... 30

4.3.11. Combining Volume Groups ............................................................................. 30

4.3.12. Backing Up Volume Group Metadata .............................................................. 31

4.3.13. Renaming a Volume Group ............................................................................ 31

4.3.14. Moving a Volume Group to Another System .................................................... 31

4.3.15. Recreating a Volume Group Directory ............................................................. 32

4.4. Logical Volume Administration ..................................................................................... 32

4.4.1. Creating Linear Logical Volumes ...................................................................... 32

4.4.2. Creating Striped Volumes ................................................................................. 34

4.4.3. Creating Mirrored Volumes ............................................................................... 34

4.4.4. Creating Snapshot Volumes ............................................................................. 39

4.4.5. Merging Snapshot Volumes .............................................................................. 41

4.4.6. Persistent Device Numbers .............................................................................. 41

4.4.7. Resizing Logical Volumes ................................................................................ 42

4.4.8. Changing the Parameters of a Logical Volume Group ........................................ 42

4.4.9. Renaming Logical Volumes .............................................................................. 42

4.4.10. Removing Logical Volumes ............................................................................ 42

4.4.11. Displaying Logical Volumes ............................................................................ 43

4.4.12. Growing Logical Volumes ............................................................................... 43

4.4.13. Shrinking Logical Volumes .............................................................................. 47

4.5. Controlling LVM Device Scans with Filters ................................................................... 47

4.6. Online Data Relocation ............................................................................................... 48

4.7. Activating Logical Volumes on Individual Nodes in a Cluster .......................................... 49

4.8. Customized Reporting for LVM .................................................................................... 49

4.8.1. Format Control ................................................................................................ 49

4.8.2. Object Selection .............................................................................................. 51

4.8.3. Sorting LVM Reports ........................................................................................ 57

4.8.4. Specifying Units ............................................................................................... 57

5. LVM Configuration Examples 59

5.1. Creating an LVM Logical Volume on Three Disks ......................................................... 59

5.1.1. Creating the Physical Volumes ......................................................................... 59

5.1.2. Creating the Volume Group .............................................................................. 59

5.1.3. Creating the Logical Volume ............................................................................. 59

5.1.4. Creating the File System .................................................................................. 59

5.2. Creating a Striped Logical Volume .............................................................................. 60

5.2.1. Creating the Physical Volumes ......................................................................... 60

5.2.2. Creating the Volume Group .............................................................................. 60

5.2.3. Creating the Logical Volume ............................................................................. 61

5.2.4. Creating the File System .................................................................................. 61

5.3. Splitting a Volume Group ............................................................................................ 61

5.3.1. Determining Free Space .................................................................................. 62

5.3.2. Moving the Data .............................................................................................. 62

5.3.3. Splitting the Volume Group ............................................................................... 62

5.3.4. Creating the New Logical Volume ..................................................................... 63

5.3.5. Making a File System and Mounting the New Logical Volume ............................. 63

5.3.6. Activating and Mounting the Original Logical Volume .......................................... 63

5.4. Removing a Disk from a Logical Volume ..................................................................... 63

5.4.1. Moving Extents to Existing Physical Volumes .................................................... 64

5.4.2. Moving Extents to a New Disk .......................................................................... 64

5.5. Creating a Mirrored LVM Logical Volume in a Cluster ................................................... 66

6. LVM Troubleshooting 69

6.1. Troubleshooting Diagnostics ........................................................................................ 69

iv

6.2. Displaying Information on Failed Devices ..................................................................... 69

6.3. Recovering from LVM Mirror Failure ............................................................................ 70

6.4. Recovering Physical Volume Metadata ........................................................................ 73

6.5. Replacing a Missing Physical Volume .......................................................................... 74

6.6. Removing Lost Physical Volumes from a Volume Group ............................................... 75

6.7. Insufficient Free Extents for a Logical Volume .............................................................. 75

7. LVM Administration with the LVM GUI 77

A. The Device Mapper 79

A.1. Device Table Mappings .............................................................................................. 79

A.1.1. The linear Mapping Target ............................................................................... 80

A.1.2. The striped Mapping Target ............................................................................. 80

A.1.3. The mirror Mapping Target ............................................................................... 82

A.1.4. The snapshot and snapshot-origin Mapping Targets .......................................... 83

A.1.5. The error Mapping Target ................................................................................ 85

A.1.6. The zero Mapping Target ................................................................................. 85

A.1.7. The multipath Mapping Target .......................................................................... 86

A.1.8. The crypt Mapping Target ................................................................................ 88

A.2. The dmsetup Command ............................................................................................. 89

A.2.1. The dmsetup info Command ............................................................................ 89

A.2.2. The dmsetup ls Command ............................................................................... 90

A.2.3. The dmsetup status Command ........................................................................ 91

A.2.4. The dmsetup deps Command .......................................................................... 91

A.3. Device Mapper Support for the udev Device Manager .................................................. 92

A.3.1. udev Integration with the Device Mapper .......................................................... 92

A.3.2. Commands and Interfaces that Support udev .................................................... 94

B. The LVM Configuration Files 97

B.1. The LVM Configuration Files ....................................................................................... 97

B.2. Sample lvm.conf File .................................................................................................. 97

C. LVM Object Tags 109

C.1. Adding and Removing Object Tags ........................................................................... 109

C.2. Host Tags ................................................................................................................ 109

C.3. Controlling Activation with Tags ................................................................................. 110

D. LVM Volume Group Metadata 111

D.1. The Physical Volume Label ...................................................................................... 111

D.2. Metadata Contents ................................................................................................... 111

D.3. Sample Metadata ..................................................................................................... 112

E. Revision History 115

Index 117

v

vi

Introduction

1. About This Guide

This book describes the Logical Volume Manager (LVM), including information on running LVM in a clustered environment.

2. 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 and GFS2 file system administration.

3. Software Versions

Table 1. Software Versions

Software Description refers to Red Hat Enterprise Linux 6 and higher Red Hat Enterprise

Linux 6

GFS2 refers to GFS2 for Red Hat Enterprise Linux 6 and higher

4. Related Documentation

For more information about using Red Hat Enterprise Linux, refer to 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, refer to 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.

vii

Introduction

• Release Notes — Provides information about the current release of Red Hat products.

High Availability Add-On documentation and other Red Hat documents are available in HTML,

PDF, and RPM versions on the Red Hat Enterprise Linux Documentation CD and online at http:// docs.redhat.com/docs/en-US/index.html

.

5. 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 (2011-11-14-15:20)

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, please include the section number and some of the surrounding text so we can find it easily.

6. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.

In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts 1

set. The

Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includes the Liberation Fonts set by default.

6.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.

Mono-spaced Bold

Used to highlight system input, including shell commands, file names and paths. Also used to highlight keycaps and key combinations. For example:

To see the contents of the file my_next_bestselling_novel in your current working directory, enter the cat my_next_bestselling_novel command at the shell prompt and press Enter to execute the command.

The above includes a file name, a shell command and a keycap, all presented in mono-spaced bold and all distinguishable thanks to context.

Key combinations can be distinguished from keycaps by the hyphen connecting each part of a key combination. For example:

Press Enter to execute the command.

1

https://fedorahosted.org/liberation-fonts/ viii

Typographic Conventions

Press Ctrl+Alt+F2 to switch to the first virtual terminal. Press Ctrl+Alt+F1 to return to your X-Windows session.

The first paragraph highlights the particular keycap to press. The second highlights two key combinations (each a set of three keycaps with each set pressed simultaneously).

If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:

File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions.

Proportional Bold

This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:

Choose System → Preferences → Mouse from the main menu bar to launch Mouse

Preferences. In the Buttons tab, click the Left-handed mouse check box and click

Close to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).

To insert a special character into a gedit file, choose Applications → Accessories

→ Character Map from the main menu bar. Next, choose Search → Find… from the

Character Map menu bar, type the name of the character in the Search field and click

Next. The character you sought will be highlighted in the Character Table. Doubleclick this highlighted character to place it in the Text to copy field and then click the

Copy button. Now switch back to your document and choose Edit → Paste from the

gedit menu bar.

The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in proportional bold and all distinguishable by context.

Mono-spaced Bold Italic or Proportional Bold Italic

Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:

To connect to a remote machine using ssh, type ssh username@domain.name at a shell prompt. If the remote machine is example.com and your username on that machine is john, type ssh [email protected].

The mount -o remount file-system command remounts the named file system. For example, to remount the /home file system, the command is mount -o remount /home .

To see the version of a currently installed package, use the rpm -q package command. It will return a result as follows: package-version-release.

Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.

Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example: ix

Introduction

Publican is a DocBook publishing system.

6.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.

Output sent to a terminal is set in mono-spaced roman and presented thus: books Desktop documentation drafts mss photos stuff svn books_tests Desktop1 downloads images notes scripts svgs

Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows: package org.

jboss .

book .

jca .

ex1 ; import javax.naming.InitialContext; public class ExClient

{ public static void main (String args[]) throws Exception

{

InitialContext iniCtx = new InitialContext();

Object ref = iniCtx.

lookup ( "EchoBean" );

EchoHome home = (EchoHome) ref;

Echo echo = home.

create ();

System.

out .

println ( "Created Echo" );

System.

out .

println ( "Echo.echo('Hello') = " + echo.

echo ( "Hello" ));

}

}

6.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring a box labeled 'Important' will not cause data loss but may cause irritation and frustration.

x

Notes and Warnings

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

xi

xii

Chapter 1.

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).

1.1. 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.

1.1.1. 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 4.4.3.1, “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 4.4.3.3, “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 4.4.5, “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 4.4.3.2, “Splitting Off a Redundant

Image of a Mirrored Logical Volume” .

1

2

Chapter 1. The LVM Logical Volume Manager

• 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 4.4.3, “Creating Mirrored Volumes” .

1.1.2. 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 4.4.4, “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 4.4.12.2, “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 C.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 C, 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 4.4.3, “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 4.7, “Activating

Logical Volumes on Individual Nodes in a Cluster”

.

1.1.3. 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, refer to the inline documentation for the /etc/ lvm/lvm.conf

file, which is also documented in Appendix B, The LVM Configuration Files

.

1.2. Logical Volumes

LVM Architecture Overview

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

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.

1.3. 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

3

Chapter 1. The LVM Logical Volume Manager

• 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 1.1, “LVM Logical Volume Components” shows the components of a simple LVM logical

volume:

4

Figure 1.1. LVM Logical Volume Components

For detailed information on the components of an LVM logical volume, see Chapter 2, LVM

Components .

1.4. 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.

The Clustered Logical Volume Manager (CLVM)

• 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:

# 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 4, LVM Administration with CLI Commands

and Chapter 7, 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 4.3.2, “Creating

Volume Groups in a Cluster”

and

Section 4.3.7, “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 1.2, “CLVM Overview”

shows a CLVM overview in a cluster.

5

Chapter 1. The LVM Logical Volume Manager

Figure 1.2. 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

.

6

1.5. Document Overview

This remainder of this document includes the following chapters:

•

Chapter 2, LVM Components

describes the components that make up an LVM logical volume.

Document Overview

•

Chapter 3, 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 4, 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 5, LVM Configuration Examples

provides a variety of LVM configuration examples.

•

Chapter 6, LVM Troubleshooting provides instructions for troubleshooting a variety of LVM issues.

•

Chapter 7, LVM Administration with the LVM GUI summarizes the operating of the LVM GUI.

•

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 C, LVM Object Tags

describes LVM object tags and host tags.

•

Appendix D, LVM Volume Group Metadata describes LVM volume group metadata, and includes a

sample copy of metadata for an LVM volume group.

7

8

Chapter 2.

LVM Components

This chapter describes the components of an LVM Logical volume.

2.1. 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 D, LVM Volume Group Metadata .

2.1.1. LVM Physical Volume Layout

Figure 2.1, “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.

9

Chapter 2. LVM Components

Figure 2.1. Physical Volume layout

2.1.2. 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.

2.2. 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.

10

LVM Logical Volumes

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.

2.3. 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.

2.3.1. Linear Volumes

A linear volume aggregates multiple 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 2.2, “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 2.2. Extent Mapping

The physical volumes that make up a logical volume do not have to be the same size. Figure 2.3,

“Linear Volume with Unequal Physical Volumes” shows volume group VG1 with a physical extent size

11

Chapter 2. LVM Components 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 100 extents in size

(400MB) and PV2 is 200 extents in size (800MB). 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 2.3. 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 2.4, “Multiple Logical Volumes”

shows the same volume group as in

Figure 2.3, “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 2.4. Multiple Logical Volumes

2.3.2. 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

12

Mirrored Logical Volumes 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 round-robin 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 2.5. 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 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 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 4.4.12.1, “Extending a Striped Volume” .

2.3.3. Mirrored Logical Volumes

13

Chapter 2. LVM Components

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 2.6, “Mirrored Logical Volume” shows a mirrored logical volume with one mirror. In this

configuration, the log is maintained on disk.

Figure 2.6. Mirrored Logical Volume

For information on creating and modifying mirrors, see

Section 4.4.3, “Creating Mirrored Volumes”

.

2.3.4. 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

LVM snapshots are not supported across the nodes in a cluster. You cannot create a snapshot volume in a clustered volume group.

14

Snapshot Volumes

Note

LVM snapshots are not supported for LVM mirrored logical volumes.

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.

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 4.4.4, “Creating Snapshot Volumes”

.

15

Chapter 2. LVM Components

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 4.4.5, “Merging Snapshot Volumes”

.

16

Chapter 3.

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 5, LVM

Configuration Examples .

For descriptions of the CLI commands you can use to perform LVM administration, see

Chapter 4,

LVM Administration with CLI Commands

. Alternately, you can use the LVM GUI, which is described in

Chapter 7, LVM Administration with the LVM GUI .

3.1. 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 1.4, “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 4.3.2, “Creating

Volume Groups in a Cluster”

and

Section 4.3.7, “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 5.5, “Creating a Mirrored

LVM Logical Volume in a Cluster” .

3.2. Logical Volume Creation Overview

17

Chapter 3. 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 single-node 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.

3.3. 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.

3.4. 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

18

Logging in the /etc/lvm/backup file and the metadata archives are stored in the /etc/lvm/archive file. How 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 4.3.12, “Backing Up Volume Group Metadata”

.

3.5. 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 .

19

20

Chapter 4.

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 3.1, “Creating LVM Volumes in a Cluster”

.

4.1. 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).

21

Chapter 4. LVM Administration with CLI Commands

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

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 6.4, “Recovering Physical Volume Metadata”

.

4.2. Physical Volume Administration

This section describes the commands that perform the various aspects of physical volume administration.

4.2.1. Creating Physical Volumes

22

Creating Physical Volumes

The following subsections describe the commands used for creating physical volumes.

4.2.1.1. 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:

# dd if=/dev/zero of=PhysicalVolume bs=512 count=1

4.2.1.2. 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

4.2.1.3. 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 [ 16.00 MB]

/dev/sda [ 17.15 GB]

/dev/root [ 13.69 GB]

/dev/ram [ 16.00 MB]

/dev/sda1 [ 17.14 GB] LVM physical volume

/dev/VolGroup00/LogVol01 [ 512.00 MB]

/dev/ram2 [ 16.00 MB]

/dev/new_vg/lvol0 [ 52.00 MB]

/dev/ram3 [ 16.00 MB]

/dev/pkl_new_vg/sparkie_lv [ 7.14 GB]

/dev/ram4 [ 16.00 MB]

/dev/ram5 [ 16.00 MB]

/dev/ram6 [ 16.00 MB]

/dev/ram7 [ 16.00 MB]

23

Chapter 4. LVM Administration with CLI Commands

/dev/ram8 [ 16.00 MB]

/dev/ram9 [ 16.00 MB]

/dev/ram10 [ 16.00 MB]

/dev/ram11 [ 16.00 MB]

/dev/ram12 [ 16.00 MB]

/dev/ram13 [ 16.00 MB]

/dev/ram14 [ 16.00 MB]

/dev/ram15 [ 16.00 MB]

/dev/sdb [ 17.15 GB]

/dev/sdb1 [ 17.14 GB] LVM physical volume

/dev/sdc [ 17.15 GB]

/dev/sdc1 [ 17.14 GB] LVM physical volume

/dev/sdd [ 17.15 GB]

/dev/sdd1 [ 17.14 GB] LVM physical volume

7 disks

17 partitions

0 LVM physical volume whole disks

4 LVM physical volumes

4.2.2. 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 4.8,

“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, etc.) 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 lvm2 [964.00 MB / 0 free]

PV /dev/sdc1 VG vg0 lvm2 [964.00 MB / 428.00 MB free]

PV /dev/sdc2 lvm2 [964.84 MB]

Total: 3 [2.83 GB] / in use: 2 [1.88 GB] / in no VG: 1 [964.84 MB]

24

Preventing Allocation on a Physical Volume

You can define a filter in the lvm.conf so that this command will avoid scanning specific physical

volumes. For information on using filters to control which devices are scanned, see Section 4.5,

“Controlling LVM Device Scans with Filters”

.

4.2.3. 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

You can also use the -xy arguments of the pvchange command to allow allocation where it had previously been disallowed.

4.2.4. 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.

4.2.5. 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 4.3.6, “Removing Physical

Volumes from a Volume Group”

.

# pvremove /dev/ram15

Labels on physical volume "/dev/ram15" successfully wiped

4.3. Volume Group Administration

This section describes the commands that perform the various aspects of volume group administration.

4.3.1. 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.

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Chapter 4. LVM Administration with CLI Commands

# 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.

The contiguous policy requires that new extents are adjacent to existing extents. 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 cling policy places new extents on the same physical volume as existing extents in the same stripe of the logical volume. These policies can be changed using the vgchange command.

For 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 4.4.12.2, “Extending a Logical

Volume with the cling Allocation Policy”

.

In general, allocation policies other than normal are required only in special cases where you need to specify unusual or nonstandard extent allocation.

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 lvo1, lvo2, and lvo3, this create six device special files:

/dev/myvg1/lv01

/dev/myvg1/lv02

/dev/myvg1/lv03

/dev/myvg2/lv01

/dev/myvg2/lv02

/dev/myvg2/lv03

The maximum device size with LVM is 8 Exabytes on 64-bit CPUs.

4.3.2. Creating Volume Groups in a Cluster

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Adding Physical Volumes to a Volume Group

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 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

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 4.3.7, “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.

[root@doc-07]# vgs

VG #PV #LV #SN Attr VSize VFree

VolGroup00 1 2 0 wz--n- 19.88G 0

testvg1 1 1 0 wz--nc 46.00G 8.00M

For more information on the vgs command, see

Section 4.3.4, “Displaying Volume

Groups”Section 4.8, “Customized Reporting for LVM”

, and the vgs man page.

4.3.3. 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

4.3.4. 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 4.3.5,

“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.

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For information on using the vgs command to customize your output, see

Section 4.8, “Customized

Reporting for LVM” .

The vgdisplay command displays volume group properties (such as size, extents, number of physical volumes, etc.) 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 new_vg

System ID

Format lvm2

Metadata Areas 3

Metadata Sequence No 11

VG Access read/write

VG Status resizable

MAX LV 0

Cur LV 1

Open LV 0

Max PV 0

Cur PV 3

Act PV 3

VG Size 51.42 GB

PE Size 4.00 MB

Total PE 13164

Alloc PE / Size 13 / 52.00 MB

Free PE / Size 13151 / 51.37 GB

VG UUID jxQJ0a-ZKk0-OpMO-0118-nlwO-wwqd-fD5D32

4.3.5. 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 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 4.5, “Controlling LVM

Device Scans with Filters”

.

The following example shows the output of a vgscan command.

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Removing Physical Volumes from a Volume Group

# 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

4.3.6. 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

-- 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

4.3.7. Changing the Parameters of a Volume Group

The vgchange command is used to deactivate and activate volume groups, as described in

Section 4.3.8, “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.

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4.3.8. 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

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 singlehost 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 4.4.8, “Changing the Parameters of a Logical Volume Group”

, For information on activating

logical volumes on individual nodes in a cluster, see Section 4.7, “Activating Logical Volumes on

Individual Nodes in a Cluster” .

4.3.9. Removing Volume Groups

To remove a volume group that contains no logical volumes, use the vgremove command.

# vgremove officevg

Volume group "officevg" successfully removed

4.3.10. 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"

4.3.11. 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

30

Backing Up Volume Group Metadata 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

4.3.12. 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.

For an example of using the vgcfgrestore command to recover physical volume metadata, see

Section 6.4, “Recovering Physical Volume Metadata”

.

4.3.13. 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

4.3.14. 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.

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.

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Chapter 4. LVM Administration with CLI Commands

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.

[root@tng3-1]# pvscan

PV /dev/sda1 is in exported VG myvg [17.15 GB / 7.15 GB free]

PV /dev/sdc1 is in exported VG myvg [17.15 GB / 15.15 GB free]

PV /dev/sdd1 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.

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.

4.3.15. 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.

4.4. Logical Volume Administration

This section describes the commands that perform the various aspects of logical volume administration.

4.4.1. 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.

The following command creates a logical volume 10 gigabytes in size in the volume group vg1.

# lvcreate -L 10G vg1

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Creating Linear Logical Volumes

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 -L1500 -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 testvol.

# 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 testvol .

# 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 4.3.6,

“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

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Chapter 4. LVM Administration with CLI Commands

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/sda1:0-25:100-

The 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 4.3.1, “Creating Volume Groups” .

4.4.2. 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 2.3.2, “Striped Logical

Volumes” .

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

4.4.3. Creating Mirrored Volumes

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Creating Mirrored Volumes

Mirrored LVM Logical Volumes 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. For an example of creating a mirrored volume in a cluster, see

Section 5.5, “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.

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

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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 re-synced 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.

# 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.

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Creating Mirrored Volumes

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

Note

As of the Red Hat Enterprise Linux 6.1 release, you can 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.

4.4.3.1. 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.

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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, refer to Section 6.3,

“Recovering from LVM Mirror Failure” .

4.4.3.2. 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

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

4.4.3.3. 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

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Creating Snapshot Volumes specified by the mirror_log_fault_policy and mirror_device_fault_policy parameters in the lvm.conf file.

4.4.3.4. Changing Mirrored Volume Configuration

You can convert a logical volume from a mirrored volume to a linear volume or from a linear volume to a mirrored volume with the lvconvert command. You can also use this command to reconfigure other mirror parameters of an existing logical volume, such as corelog.

When you convert a logical volume to a mirrored volume, you are basically 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 6.3, “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

4.4.4. Creating Snapshot Volumes

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 4.7, “Activating Logical Volumes on Individual Nodes in a

Cluster” .

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Chapter 4. LVM Administration with CLI Commands

Note

As of the Red Hat Enterprise Linux 6.1 release, LVM snapshots are supported for mirrored logical volumes.

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

LV Size 52.00 MB

Current LE 13

Segments 1

Allocation inherit

Read ahead sectors 0

Block device 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

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Merging Snapshot Volumes

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.

4.4.5. 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 C, LVM Object Tags

. For further information on the lvconvert --merge command, see the lvconvert(8) man page.

4.4.6. 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

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.

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4.4.7. Resizing Logical Volumes

To reduce the size of a logical volume, use the lvreduce command. If the logical volume contains a file system, be sure to reduce the file system first (or use the LVM GUI) so that the logical volume is always at least as large as the file system expects it to be.

The following command reduces the size of logical volume lvol1 in volume group vg00 by 3 logical extents.

# lvreduce -l -3 vg00/lvol1

4.4.8. 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 4.3.7, “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

4.4.9. 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 4.7,

“Activating Logical Volumes on Individual Nodes in a Cluster”

.

4.4.10. 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.

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Displaying Logical Volumes

[root@tng3-1 lvm]# 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.

4.4.11. Displaying Logical Volumes

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 4.8, “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

4.4.12. 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.

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Chapter 4. LVM Administration with CLI Commands

# 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.

[root@tng3-1 ~]# lvextend -l +100%FREE /dev/myvg/testlv

Extending logical volume testlv to 68.59 GB

Logical volume testlv successfully resized

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.

4.4.12.1. 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 #PV #LV #SN Attr VSize VFree

vg 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% Devices

stripe1 vg -wi-a- 271.31G /dev/sda1(0),/dev/sdb1(0)

Note that the volume group now has no more free space.

# vgs

VG #PV #LV #SN Attr VSize VFree

vg 2 1 0 wz--n- 271.31G 0

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Growing Logical Volumes

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

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

4.4.12.2. 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.

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Chapter 4. LVM Administration with CLI Commands

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" ]

For information on tagging physical volumes, see

Appendix C, 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.

[root@taft-03 ~]# pvs -a -o +pv_tags /dev/sd[bcdefgh]1

PV VG Fmt Attr PSize PFree PV Tags

/dev/sdb1 taft lvm2 a- 135.66g 135.66g A

/dev/sdc1 taft lvm2 a- 135.66g 135.66g B

/dev/sdd1 taft lvm2 a- 135.66g 135.66g B

/dev/sde1 taft lvm2 a- 135.66g 135.66g C

/dev/sdf1 taft lvm2 a- 135.66g 135.66g C

/dev/sdg1 taft lvm2 a- 135.66g 135.66g A

/dev/sdh1 taft lvm2 a- 135.66g 135.66g A

The following command creates a 100GB mirrored volume from the volume group taft.

[root@taft-03 ~]# lvcreate -m 1 -n mirror --nosync -L 100G taft

The following command shows which devices are used for the mirror legs and mirror log.

[root@taft-03 ~]# 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.

[root@taft-03 ~]# 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.

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Shrinking Logical Volumes

[root@taft-03 ~]# 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)

[mirror_mimage_0] taft Iwi-ao 200.00g /dev/sdb1(0)

[mirror_mimage_0] taft Iwi-ao 200.00g /dev/sdg1(0)

[mirror_mimage_1] taft Iwi-ao 200.00g /dev/sdc1(0)

[mirror_mimage_1] taft Iwi-ao 200.00g /dev/sdd1(0)

[mirror_mlog] taft lwi-ao 4.00m /dev/sdh1(0)

4.4.13. Shrinking Logical Volumes

To reduce the size of a logical volume, first unmount the file system. You can then use the lvreduce command to shrink the volume. After shrinking the volume, remount the file system.

Warning

It is important to reduce the size of the file system or whatever is residing in the volume before shrinking the volume itself, otherwise you risk losing data.

Shrinking a logical volume frees some of the volume group to be allocated to other logical volumes in the volume group.

The following example reduces the size of logical volume lvol1 in volume group vg00 by 3 logical extents.

# lvreduce -l -3 vg00/lvol1

4.5. 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 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:

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Chapter 4. LVM Administration with CLI Commands filter = [ "a/.*/" ]

The following filter removes the cdrom device in order to avoid delays if the drive contains no media: 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/.*/" ]

For more information on the lvm.conf file, see

Appendix B, The LVM Configuration Files and the

lvm.conf

(5) man page.

4.6. 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.

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

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.

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Activating Logical Volumes on Individual Nodes in a Cluster

# pvmove -i5 /dev/sdd1

4.7. 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 C, LVM Object Tags

. You can also specify activation of nodes in the configuration file, which is described in

Appendix B, The LVM Configuration Files .

4.8. 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.

4.8.1. 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

/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

The following command displays only the physical volume name and size.

# pvs -o pv_name,pv_size

PV PSize

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Chapter 4. LVM Administration with CLI Commands

/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 Fmt Attr PSize PFree PV UUID

/dev/sdb1 new_vg lvm2 a- 17.14G 17.14G onFF2w-1fLC-ughJ-D9eB-M7iv-6XqA-dqGeXY

/dev/sdc1 new_vg lvm2 a- 17.14G 17.09G Joqlch-yWSj-kuEn-IdwM-01S9-X08M-mcpsVe

/dev/sdd1 new_vg lvm2 a- 17.14G 17.14G yvfvZK-Cf31-j75k-dECm-0RZ3-0dGW-UqkCS

• 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 a- 17.14G 17.14G 17.14G onFF2w-1fLC-ughJ-D9eB-M7iv-6XqA-dqGeXY

/dev/sdc1 new_vg lvm2 a- 17.14G 17.09G 17.14G Joqlch-yWSj-kuEn-IdwM-01S9-XO8M-mcpsVe

/dev/sdd1 new_vg lvm2 a- 17.14G 17.14G 17.14G yvfvZK-Cf31-j75k-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

(=).

# 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.

50

# 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

Object Selection

/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 6.2, “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 PV

new_vg 3 1 0 wz--n- 51.42G 51.37G /dev/sdc1

new_vg 3 1 0 wz--n- 51.42G 51.37G /dev/sdd1

new_vg 3 1 0 wz--n- 51.42G 51.37G /dev/sdb1

4.8.2. 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

The pvs Command

Table 4.1, “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 4.1. pvs Display Fields

Argument dev_size pe_start pv_attr pv_fmt pv_free

Header

DevSize

1st PE

Attr

Fmt

PFree

Description

The size of the underlying device on which the physical volume was created

Offset to the start of the first physical extent in the underlying device

Status of the physical volume: (a)llocatable or e(x)ported.

The metadata format of the physical volume (lvm2 or lvm1 )

The free space remaining on the physical volume

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Argument pv_name pv_pe_alloc_count pv_pe_count pvseg_size pvseg_start pv_size pv_tags pv_used

Header

PV

Alloc

PE

SSize

Start

PSize

PV Tags

Used

Description

The physical volume name

Number of used physical extents

Number of physical extents

The segment size of the physical volume

The starting physical extent of the physical volume segment

The size of the physical volume

LVM tags attached to the physical volume

The amount of space currently used on the physical volume

The UUID of the physical volume pv_uuid PV UUID

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 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 17.13G

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 a- 17.14G 17.14G 17.14G onFF2w-1fLC-ughJ-D9eB-M7iv-6XqA-dqGeXY

/dev/sdc1 new_vg lvm2 a- 17.14G 17.09G 17.14G Joqlch-yWSj-kuEn-IdwM-01S9-XO8M-mcpsVe

/dev/sdd1 new_vg lvm2 a- 17.14G 17.13G 17.14G yvfvZK-Cf31-j75k-dECm-0RZ3-0dGW-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 Fmt Attr PSize PFree Start SSize

/dev/hda2 VolGroup00 lvm2 a- 37.16G 32.00M 0 1172

/dev/hda2 VolGroup00 lvm2 a- 37.16G 32.00M 1172 16

/dev/hda2 VolGroup00 lvm2 a- 37.16G 32.00M 1188 1

/dev/sda1 vg lvm2 a- 17.14G 16.75G 0 26

/dev/sda1 vg lvm2 a- 17.14G 16.75G 26 24

/dev/sda1 vg lvm2 a- 17.14G 16.75G 50 26

/dev/sda1 vg lvm2 a- 17.14G 16.75G 76 24

/dev/sda1 vg lvm2 a- 17.14G 16.75G 100 26

/dev/sda1 vg lvm2 a- 17.14G 16.75G 126 24

/dev/sda1 vg lvm2 a- 17.14G 16.75G 150 22

/dev/sda1 vg lvm2 a- 17.14G 16.75G 172 4217

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Object Selection

/dev/sdb1 vg lvm2 a- 17.14G 17.14G 0 4389

/dev/sdc1 vg lvm2 a- 17.14G 17.14G 0 4389

/dev/sdd1 vg lvm2 a- 17.14G 17.14G 0 4389

/dev/sde1 vg lvm2 a- 17.14G 17.14G 0 4389

/dev/sdf1 vg lvm2 a- 17.14G 17.14G 0 4389

/dev/sdg1 vg lvm2 a- 17.14G 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

PV VG Fmt Attr PSize PFree

/dev/VolGroup00/LogVol01 -- 0 0

/dev/new_vg/lvol0 -- 0 0

/dev/ram -- 0 0

/dev/ram0 -- 0 0

/dev/ram2 -- 0 0

/dev/ram3 -- 0 0

/dev/ram4 -- 0 0

/dev/ram5 -- 0 0

/dev/ram6 -- 0 0

/dev/root -- 0 0

/dev/sda -- 0 0

/dev/sdb -- 0 0

/dev/sdb1 new_vg lvm2 a- 17.14G 17.14G

/dev/sdc -- 0 0

/dev/sdc1 new_vg lvm2 a- 17.14G 17.09G

/dev/sdd -- 0 0

/dev/sdd1 new_vg lvm2 a- 17.14G 17.14G

The vgs Command

Table 4.2, “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 4.2. vgs Display Fields

Argument lv_count max_lv max_pv pv_count snap_count vg_attr vg_extent_count vg_extent_size vg_fmt vg_free

Header

#LV

MaxLV

MaxPV

#PV

#SN

Attr

#Ext

Ext

Fmt

VFree

Description

The number of logical volumes the volume group contains

The maximum number of logical volumes allowed in the volume group (0 if unlimited)

The maximum number of physical volumes allowed in the volume group (0 if unlimited)

The number of physical volumes that define the volume group

The number of snapshots the volume group contains

Status of the volume group: (w)riteable, (r)eadonly, resi(z)eable, e(x)ported, (p)artial and (c)lustered.

The number of physical extents in the volume group

The size of the physical extents in the volume group

The metadata format of the volume group (lvm2 or lvm1 )

Size of the free space remaining in the volume group

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Argument vg_free_count vg_name vg_seqno vg_size vg_sysid vg_tags vg_uuid

Header

Free

VG

Seq

VSize

SYS ID

VG Tags

VG UUID

Description

Number of free physical extents in the volume group

The volume group name

Number representing the revision of the volume group

The size of the volume group

LVM1 System ID

LVM tags attached to the volume group

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-0118-nlwO-wwqd-fD5D32

The lvs Command

Table 4.3, “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 4.3. lvs Display Fields

Argument chunksize chunk_size copy_percent devices lv_attr

Header

Chunk

Copy%

Devices

Attr

Description

Unit size in a snapshot volume

The synchronization percentage of a mirrored logical volume; also used when physical extents are being moved with the pv_move command

The underlying devices that make up the logical volume: the physical volumes, logical volumes, and start physical extents and logical extents

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, (p)vmove, (s)napshot, invalid (S)napshot,

(v)irtual

Bit 2: Permissions: (w)riteable, (r)ead-only

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Object Selection

Argument lv_kernel_major lv_kernel_minor lv_major lv_minor lv_name lv_size lv_tags lv_uuid mirror_log modules move_pv

Header

KMaj

KMIN

Maj

Min

LV

LSize

LV Tags

LV UUID

Log

Modules

Move

Description

Bit 3: Allocation policy: (c)ontiguous, (n)ormal,

(a)nywhere, (i)nherited. 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, mapped (d)evice present without tables, mapped device present with (i)nactive table

Bit 6: device (o)pen

Actual major device number of the logical volume (-1 if inactive)

Actual minor device number of the logical volume (-1 if inactive)

The persistent major device number of the logical volume (-1 if not specified)

The persistent minor device number of the logical volume (-1 if not specified)

The name of the logical volume

The size of the logical volume

LVM tags attached to the logical volume

The UUID of the logical volume.

Device on which the mirror log resides

Corresponding kernel device-mapper target necessary to use this logical volume

Source physical volume of a temporary logical volume created with the pvmove command

The origin device of a snapshot volume

The unit size of a mirrored logical volume origin regionsize region_size seg_count seg_size seg_start seg_tags segtype snap_percent stripes stripesize stripe_size

Origin

Region

#Seg

SSize

Start

Seg Tags

Type

Snap%

#Str

Stripe

The number of segments in the logical volume

The size of the segments in the logical volume

Offset of the segment in the logical volume

LVM tags attached to the segments of the logical volume

The segment type of a logical volume (for example: mirror, striped, linear)

Current percentage of a snapshot volume that is in use

Number of stripes or mirrors in a logical volume

Unit size of the stripe in a striped logical volume

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.

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# lvs

LV VG Attr LSize Origin Snap% Move Log Copy% Convert

lvol0 new_vg owi-a- 52.00M

newvgsnap1 new_vg swi-a- 8.00M lvol0 0.20

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

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 Attr #Str Type SSize

LogVol00 VolGroup00 -wi-ao 1 linear 36.62G

LogVol01 VolGroup00 -wi-ao 1 linear 512.00M

lv vg -wi-a- 1 linear 104.00M

lv vg -wi-a- 1 linear 104.00M

lv vg -wi-a- 1 linear 104.00M

lv vg -wi-a- 1 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-a- 0 52.00M 1 linear 0 0

newvgsnap1 new_vg swi-a- 0 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% Move Log Copy%

lvol0 new_vg -wi-a- 52.00M

# lvs --segments

LV VG Attr #Str Type SSize

lvol0 new_vg -wi-a- 1 linear 52.00M

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Sorting LVM Reports

4.8.3. 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

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

4.8.4. 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.

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# pvs --units m

PV VG Fmt Attr PSize PFree

/dev/sda1 lvm2 -- 17555.40M 17555.40M

/dev/sdb1 new_vg lvm2 a- 17552.00M 17552.00M

/dev/sdc1 new_vg lvm2 a- 17552.00M 17500.00M

/dev/sdd1 new_vg lvm2 a- 17552.00M 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 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

The following command displays the output as a multiple of 1000.

# pvs --units G

PV VG Fmt Attr PSize PFree

/dev/sdb1 new_vg lvm2 a- 18.40G 18.40G

/dev/sdc1 new_vg lvm2 a- 18.40G 18.35G

/dev/sdd1 new_vg lvm2 a- 18.40G 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 Fmt Attr PSize PFree

/dev/sdb1 new_vg lvm2 a- 35946496S 35946496S

/dev/sdc1 new_vg lvm2 a- 35946496S 35840000S

/dev/sdd1 new_vg lvm2 a- 35946496S 35946496S

The following example displays the output of the pvs command in units of 4 MB.

# pvs --units 4m

PV VG Fmt Attr PSize PFree

/dev/sdb1 new_vg lvm2 a- 4388.00U 4388.00U

/dev/sdc1 new_vg lvm2 a- 4388.00U 4375.00U

/dev/sdd1 new_vg lvm2 a- 4388.00U 4388.00U

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Chapter 5.

LVM Configuration Examples

This chapter provides some basic LVM configuration examples.

5.1. 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.

5.1.1. 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.

[root@tng3-1 ~]# pvcreate /dev/sda1 /dev/sdb1 /dev/sdc1

Physical volume "/dev/sda1" successfully created

Physical volume "/dev/sdb1" successfully created

Physical volume "/dev/sdc1" successfully created

5.1.2. Creating the Volume Group

The following command creates the volume group new_vol_group.

[root@tng3-1 ~]# 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.

[root@tng3-1 ~]# vgs

VG #PV #LV #SN Attr VSize VFree

new_vol_group 3 0 0 wz--n- 51.45G 51.45G

5.1.3. 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.

[root@tng3-1 ~]# lvcreate -L2G -n new_logical_volume new_vol_group

Logical volume "new_logical_volume" created

5.1.4. Creating the File System

The following command creates a GFS2 file system on the logical volume.

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Chapter 5. LVM Configuration Examples

[root@tng3-1 ~]# 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: /dev/new_vol_group/new_logical_volume

Blocksize: 4096

Filesystem Size: 491460

Journals: 1

Resource Groups: 8

Locking Protocol: lock_nolock

Lock Table:

Syncing...

All Done

The following commands mount the logical volume and report the file system disk space usage.

[root@tng3-1 ~]# 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

5.2. 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.

5.2.1. 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.

[root@tng3-1 ~]# pvcreate /dev/sda1 /dev/sdb1 /dev/sdc1

Physical volume "/dev/sda1" successfully created

Physical volume "/dev/sdb1" successfully created

Physical volume "/dev/sdc1" successfully created

5.2.2. Creating the Volume Group

The following command creates the volume group volgroup01.

[root@tng3-1 ~]# vgcreate volgroup01 /dev/sda1 /dev/sdb1 /dev/sdc1

Volume group "volgroup01" successfully created

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Creating the Logical Volume

You can use the vgs command to display the attributes of the new volume group.

[root@tng3-1 ~]# vgs

VG #PV #LV #SN Attr VSize VFree

volgroup01 3 0 0 wz--n- 51.45G 51.45G

5.2.3. 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.

[root@tng3-1 ~]# 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

5.2.4. Creating the File System

The following command creates a GFS2 file system on the logical volume.

[root@tng3-1 ~]# 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: /dev/volgroup01/striped_logical_volume

Blocksize: 4096

Filesystem Size: 492484

Journals: 1

Resource Groups: 8

Locking Protocol: lock_nolock

Lock Table:

Syncing...

All Done

The following commands mount the logical volume and report the file system disk space usage.

[root@tng3-1 ~]# mount /dev/volgroup01/striped_logical_volume /mnt

[root@tng3-1 ~]# df

Filesystem 1K-blocks Used Available Use% Mounted on

/dev/mapper/VolGroup00-LogVol00

13902624 1656776 11528232 13% /

/dev/hda1 101086 10787 85080 12% /boot tmpfs 127880 0 127880 0% /dev/shm

/dev/volgroup01/striped_logical_volume

1969936 20 1969916 1% /mnt

5.3. Splitting a Volume Group

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.

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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.

5.3.1. Determining Free Space

You can use the pvscan command to determine how much free space is currently available in the volume group.

[root@tng3-1 ~]# pvscan

PV /dev/sda1 VG myvg lvm2 [17.15 GB / 0 free]

PV /dev/sdb1 VG myvg lvm2 [17.15 GB / 12.15 GB free]

PV /dev/sdc1 VG myvg lvm2 [17.15 GB / 15.80 GB free]

Total: 3 [51.45 GB] / in use: 3 [51.45 GB] / in no VG: 0 [0 ]

5.3.2. 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.

[root@tng3-1 ~]# 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.

[root@tng3-1 ~]# pvscan

PV /dev/sda1 VG myvg lvm2 [17.15 GB / 0 free]

PV /dev/sdb1 VG myvg lvm2 [17.15 GB / 10.80 GB free]

PV /dev/sdc1 VG myvg lvm2 [17.15 GB / 17.15 GB free]

Total: 3 [51.45 GB] / in use: 3 [51.45 GB] / in no VG: 0 [0 ]

5.3.3. 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.

[root@tng3-1 ~]# lvchange -a n /dev/myvg/mylv

[root@tng3-1 ~]# vgsplit myvg yourvg /dev/sdc1

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Creating the New Logical Volume

Volume group "yourvg" successfully split from "myvg"

You can use the vgs command to see the attributes of the two volume groups.

[root@tng3-1 ~]# 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

5.3.4. Creating the New Logical Volume

After creating the new volume group, you can create the new logical volume yourlv.

[root@tng3-1 ~]# lvcreate -L5G -n yourlv yourvg

Logical volume "yourlv" created

5.3.5. Making a File System and Mounting the New Logical Volume

You can make a file system on the new logical volume and mount it.

[root@tng3-1 ~]# 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: /dev/yourvg/yourlv

Blocksize: 4096

Filesystem Size: 1277816

Journals: 1

Resource Groups: 20

Locking Protocol: lock_nolock

Lock Table:

Syncing...

All Done

[root@tng3-1 ~]# mount /dev/yourvg/yourlv /mnt

5.3.6. 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.

root@tng3-1 ~]# lvchange -a y 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

5.4. Removing a Disk from a Logical Volume

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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.

5.4.1. Moving Extents to Existing Physical Volumes

In this example, the logical volume is distributed across four physical volumes in the volume group myvg .

[root@tng3-1]# pvs -o+pv_used

PV VG Fmt Attr PSize PFree Used

/dev/sda1 myvg lvm2 a- 17.15G 12.15G 5.00G

/dev/sdb1 myvg lvm2 a- 17.15G 12.15G 5.00G

/dev/sdc1 myvg lvm2 a- 17.15G 12.15G 5.00G

/dev/sdd1 myvg lvm2 a- 17.15G 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.

[root@tng3-1 ~]# 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:

[root@tng3-1]# pvs -o+pv_used

PV VG Fmt Attr PSize PFree Used

/dev/sda1 myvg lvm2 a- 17.15G 7.15G 10.00G

/dev/sdb1 myvg lvm2 a- 17.15G 17.15G 0

/dev/sdc1 myvg lvm2 a- 17.15G 12.15G 5.00G

/dev/sdd1 myvg lvm2 a- 17.15G 2.15G 15.00G

Use the vgreduce command to remove the physical volume /dev/sdb1 from the volume group.

[root@tng3-1 ~]# 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 a- 17.15G 7.15G

/dev/sdb1 lvm2 -- 17.15G 17.15G

/dev/sdc1 myvg lvm2 a- 17.15G 12.15G

/dev/sdd1 myvg lvm2 a- 17.15G 2.15G

The disk can now be physically removed or allocated to other users.

5.4.2. Moving Extents to a New Disk

In this example, the logical volume is distributed across three physical volumes in the volume group myvg as follows:

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Moving Extents to a New Disk

[root@tng3-1]# pvs -o+pv_used

PV VG Fmt Attr PSize PFree Used

/dev/sda1 myvg lvm2 a- 17.15G 7.15G 10.00G

/dev/sdb1 myvg lvm2 a- 17.15G 15.15G 2.00G

/dev/sdc1 myvg lvm2 a- 17.15G 15.15G 2.00G

We want to move the extents of /dev/sdb1 to a new device, /dev/sdd1.

5.4.2.1. Creating the New Physical Volume

Create a new physical volume from /dev/sdd1.

[root@tng3-1 ~]# pvcreate /dev/sdd1

Physical volume "/dev/sdd1" successfully created

5.4.2.2. Adding the New Physical Volume to the Volume Group

Add /dev/sdd1 to the existing volume group myvg.

[root@tng3-1 ~]# 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 a- 17.15G 7.15G 10.00G

/dev/sdb1 myvg lvm2 a- 17.15G 15.15G 2.00G

/dev/sdc1 myvg lvm2 a- 17.15G 15.15G 2.00G

/dev/sdd1 myvg lvm2 a- 17.15G 17.15G 0

5.4.2.3. Moving the Data

Use the pvmove command to move the data from /dev/sdb1 to /dev/sdd1.

[root@tng3-1 ~]# pvmove /dev/sdb1 /dev/sdd1

/dev/sdb1: Moved: 10.0%

...

/dev/sdb1: Moved: 79.7%

...

/dev/sdb1: Moved: 100.0%

[root@tng3-1]# pvs -o+pv_used

PV VG Fmt Attr PSize PFree Used

/dev/sda1 myvg lvm2 a- 17.15G 7.15G 10.00G

/dev/sdb1 myvg lvm2 a- 17.15G 17.15G 0

/dev/sdc1 myvg lvm2 a- 17.15G 15.15G 2.00G

/dev/sdd1 myvg lvm2 a- 17.15G 15.15G 2.00G

5.4.2.4. 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.

[root@tng3-1 ~]# 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.

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5.5. 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 3.1, “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

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:

[root@doc-07 ~]# ps auxw | grep clvmd root 17642 0.0 0.1 32164 1072 ? Ssl Apr06 0:00 clvmd -T20 -t 90

The following command shows the local view of the cluster status:

[root@example-01 ~]# cman_tool services fence domain member count 3 victim count 0 victim now 0 master nodeid 2 wait state none members 1 2 3 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.

[root@hexample-01 ~]# service cmirrord start

Starting cmirrord: [ OK ]

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Creating a Mirrored LVM Logical Volume in a Cluster

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.

[root@doc-07 ~]# pvcreate /dev/xvdb1

Physical volume "/dev/xvdb1" successfully created

[root@doc-07 ~]# pvcreate /dev/xvdb2

Physical volume "/dev/xvdb2" successfully created

[root@doc-07 ~]# pvcreate /dev/xvdc1

Physical volume "/dev/xvdc1" 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.

[root@doc-07 ~]# vgcreate vg001 /dev/xvdb1 /dev/xvdb2 /dev/xvdc1

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.

[root@doc-07 ~]# 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.

[root@doc-07 ~]# lvcreate -l 1000 -m1 vg001 -n mirrorlv /dev/xvdb1:1-1000 /dev/ xvdb2:1-1000 /dev/xvdc1:0

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.

[root@doc-07 log]# lvs vg001/mirrorlv

LV VG Attr LSize Origin Snap% Move Log Copy% Convert

mirrorlv vg001 mwi-a- 3.91G vg001_mlog 47.00

[root@doc-07 log]# lvs vg001/mirrorlv

LV VG Attr LSize Origin Snap% Move Log Copy% Convert

mirrorlv vg001 mwi-a- 3.91G vg001_mlog 91.00

[root@doc-07 ~]# lvs vg001/mirrorlv

LV VG Attr LSize Origin Snap% Move Log Copy% Convert

mirrorlv vg001 mwi-a- 3.91G vg001_mlog 100.00

The completion of the mirror is noted in the system log:

May 10 14:52:52 doc-07 [19402]: Monitoring mirror device vg001-mirrorlv for events

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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.

[root@doc-07 ~]# lvs -a -o +devices

LV VG Attr LSize Origin Snap% Move 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/xvdb1(1)

[mirrorlv_mimage_1] vg001 iwi-ao 3.91G

/dev/xvdb2(1)

[mirrorlv_mlog] vg001 lwi-ao 4.00M

/dev/xvdc1(0)

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.

[root@doc-07 ~]# lvs -a -o +seg_pe_ranges --segments

PE Ranges

mirrorlv_mimage_0:0-999 mirrorlv_mimage_1:0-999

/dev/xvdb1:1-1000

/dev/xvdb2:1-1000

/dev/xvdc1:0-0

Note

For information on recovering from the failure of one of the legs of an LVM mirrored volume, see

Section 6.3, “Recovering from LVM Mirror Failure”

.

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Chapter 6.

LVM Troubleshooting

This chapter provide instructions for troubleshooting a variety of LVM issues.

6.1. 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 lvm dumpconfig command.

• Check the .cache file in the /etc/lvm directory for a record of which devices have physical volumes on them.

6.2. 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.

[root@link-07 tmp]# 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.

[root@link-07 tmp]# 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.

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Chapter 6. LVM Troubleshooting

[root@link-07 tmp]# lvs -a -o +devices

Volume group "vg" not found

Using the -P argument shows the logical volumes that have failed.

[root@link-07 tmp]# 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.

root@link-08 ~]# 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)

[root@link-08 ~]# 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)

6.3. 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, refer to Section 6.3,

“Recovering from LVM Mirror Failure”

.

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.

[root@link-08 ~]# pvcreate /dev/sd[abcdefgh][12]

Physical volume "/dev/sda1" successfully created

Physical volume "/dev/sda2" successfully created

Physical volume "/dev/sdb1" successfully created

Physical volume "/dev/sdb2" successfully created

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Recovering from LVM Mirror Failure

Physical volume "/dev/sdc1" successfully created

Physical volume "/dev/sdc2" successfully created

Physical volume "/dev/sdd1" successfully created

Physical volume "/dev/sdd2" successfully created

Physical volume "/dev/sde1" successfully created

Physical volume "/dev/sde2" successfully created

Physical volume "/dev/sdf1" successfully created

Physical volume "/dev/sdf2" successfully created

Physical volume "/dev/sdg1" successfully created

Physical volume "/dev/sdg2" successfully created

Physical volume "/dev/sdh1" successfully created

Physical volume "/dev/sdh2" successfully created

The following commands creates the volume group vg and the mirrored volume groupfs.

[root@link-08 ~]# 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.

[root@link-08 ~]# lvs -a -o +devices

LV VG Attr LSize Origin Snap% Move Log Copy% Devices

groupfs vg mwi-a- 752.00M groupfs_mlog 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% Move Log Copy% Devices

groupfs vg mwi-a- 752.00M groupfs_mlog 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)

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

[root@link-08 ~]# 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.

[root@link-08 ~]# 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

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Chapter 6. LVM Troubleshooting

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.

[root@link-08 ~]# 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.

[root@link-08 ~]# vgextend vg /dev/sdi[12]

Volume group "vg" successfully extended

[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 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.

[root@link-08 ~]# lvconvert -m 1 /dev/vg/groupfs /dev/sdi1 /dev/sdb1 /dev/sdc1

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Recovering Physical Volume Metadata

Logical volume mirror converted.

You can use the lvs command to verify that the mirror is restored.

[root@link-08 ~]# lvs -a -o +devices

LV VG Attr LSize Origin Snap% Move Log Copy% Devices

groupfs vg mwi-a- 752.00M groupfs_mlog 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)

6.4. 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.

Warning

You should not attempt this procedure with a working LVM logical volume. You will lose your data if you specify the incorrect UUID.

The following example shows the sort of output you may see if the metadata area is missing or corrupted.

[root@link-07 backup]# 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.

[root@link-07 backup]# 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

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Chapter 6. LVM Troubleshooting 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.

[root@link-07 backup]# 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.

[root@link-07 backup]# vgcfgrestore VG

Restored volume group VG

You can now display the logical volumes.

[root@link-07 backup]# lvs -a -o +devices

LV VG Attr LSize Origin Snap% Move Log Copy% Devices

stripe VG -wi--- 300.00G /dev/sdh1 (0),/dev/sda1(0)

stripe VG -wi--- 300.00G /dev/sdh1 (34728),/dev/sdb1(0)

The following commands activate the volumes and display the active volumes.

[root@link-07 backup]# lvchange -ay /dev/VG/stripe

[root@link-07 backup]# lvs -a -o +devices

LV VG Attr LSize Origin Snap% Move Log Copy% Devices

stripe VG -wi-a- 300.00G /dev/sdh1 (0),/dev/sda1(0)

stripe VG -wi-a- 300.00G /dev/sdh1 (34728),/dev/sdb1(0)

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.

6.5. 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 6.4, “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.

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Removing Lost Physical Volumes from a Volume Group

6.6. 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.

6.7. 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

--- 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.

[root@tng3-1 ~]# 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 run 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

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Chapter 6. LVM Troubleshooting

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 4.4.1, “Creating Linear Logical Volumes” .

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Chapter 7.

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 bring up this utility by typing system- config-lvm . 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 device-mapper 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 8:48 65920

35258368 35258368 linear 8:32 65920

70516736 17694720 linear 8:16 17694976

88211456 17694720 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 the format of the following mappings:

• linear

• striped

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• mirror

• snapshot and snapshot-origin

• error

• zero

• multipath

• crypt

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

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.

80

The striped Mapping Target 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

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.

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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: 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

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The snapshot and snapshot-origin Mapping Targets logargs the log arguments for the mirror; the number of log arguments provided is specified by the #log- args 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 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:

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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 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 ago 18:15 /dev/mapper/volumeGroup-base-real brw------- 1 root root 254, 12 29 ago 18:15 /dev/mapper/volumeGroup-snap-cow brw------- 1 root root 254, 13 29 ago 18:15 /dev/mapper/volumeGroup-snap brw------- 1 root root 254, 10 29 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

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The error Mapping Target 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

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.

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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 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.

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The multipath Mapping Target 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.

#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

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Appendix A. The Device Mapper

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.

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

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The dmsetup Command 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 is an example of a crypt target.

0 2097152 crypt aes-plain 0123456789abcdef0123456789abcdef 0 /dev/hda 0

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

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.

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.

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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.

[root@ask-07 ~]# dmsetup info

Name: testgfsvg-testgfslv1

State: ACTIVE

Read Ahead: 256

Tables present: LIVE

Open count: 0

Event number: 0

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.

[root@ask-07 ~]# dmsetup ls testgfsvg-testgfslv3 (253, 4) testgfsvg-testgfslv2 (253, 3) testgfsvg-testgfslv1 (253, 2)

VolGroup00-LogVol01 (253, 1)

VolGroup00-LogVol00 (253, 0)

The following example shows the command to list the devices names of currently configured mirror mappings.

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The dmsetup status Command

[root@grant-01 ~]# dmsetup ls --target mirror lock_stress-grant--02.1722 (253, 34) lock_stress-grant--01.1720 (253, 18) lock_stress-grant--03.1718 (253, 52) lock_stress-grant--02.1716 (253, 40) lock_stress-grant--03.1713 (253, 47) lock_stress-grant--02.1709 (253, 23) lock_stress-grant--01.1707 (253, 8) lock_stress-grant--01.1724 (253, 14) lock_stress-grant--03.1711 (253, 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)

│ └─ (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.

[root@ask-07 ~]# 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.

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The following example shows the command to list the dependencies of all currently configured mapped devices.

[root@ask-07 ~]# dmsetup deps testgfsvg-testgfslv3: 1 dependencies : (8, 16) testgfsvg-testgfslv2: 1 dependencies : (8, 16) testgfsvg-testgfslv1: 1 dependencies : (8, 16)

VolGroup00-LogVol01: 1 dependencies : (8, 2)

VolGroup00-LogVol00: 1 dependencies : (8, 2)

The following example shows the command to list the dependencies only of the device lock_stress-grant--02.1722

:

[root@grant-01 ~]# dmsetup deps lock_stress-grant--02.1722

3 dependencies : (253, 33) (253, 32) (253, 31)

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 userspace. 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

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udev Integration with the Device Mapper 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

10-dm.rules

11-dm-lvm.rules

13-dm-disk.rules

95-dm-notify.rules

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.

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.

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.

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.

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 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

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Appendix A. The Device Mapper

• 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 dmsetup udevcomplete_all

Used to notify that udev has completed processing the rules and unlocks waiting process (called from within udev rules in

95-dm-notify.rules

).

Used for debugging purposes to manually unlock all waiting processes.

dmsetup udevcookies dmsetup udevcreatecookie dmsetup udevreleasecookie

Used for debugging purposes, to show all existing cookies

(system-wide semaphores).

Used to create a cookie (semaphore) manually. This is useful to run more processes under one synchronization resource.

Used to wait for all udev processing related to all processes put under that one synchronization cookie.

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 ...

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Commands and Interfaces that Support udev

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.

95

96

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 lvm dumpconfig command.

For information on loading additional configuration files, see

Section C.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 tiles to read in. For

information on host tags, see Section C.2, “Host Tags”

.

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. Sample lvm.conf File

The following is a sample lvm.conf configuration file. Your configuration file may differ slightly from this one.

# 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

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Appendix B. The LVM Configuration Files

# the environment variable LVM_SYSTEM_DIR before running the tools.

#

# N.B. Take care that each setting only appears once if uncommenting

# example settings in this file.

# 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.

# 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 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 any name matches any 'a'

# pattern, the device is accepted; otherwise if any name matches any 'r'

# pattern 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:

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Sample lvm.conf File

# filter =[ "a|loop|", "r|/dev/hdc|", "a|/dev/ide|", "r|.*|" ]

# Use anchors if you want to be really specific

# filter = [ "a|^/dev/hda8$|", "r/.*/" ]

# 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.)

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 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

# 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.

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).

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Appendix B. The LVM Configuration Files

# 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 device-mapper

# 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 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

#

100

Sample lvm.conf File

# 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

#}

# 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

# 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

# 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

}

# 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!

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Appendix B. The LVM Configuration Files

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

# 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

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Sample lvm.conf File

# The default metadata format that commands should use - "lvm1" or "lvm2".

# The command line override is -M1 or -M2.

# 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

# 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

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Appendix B. The LVM Configuration Files

# 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. Snapshots of this type of RAID1 can be

# problematic.

#

# "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.

#

# Specify the '--type <mirror|raid1>' option to override this default

# setting.

mirror_segtype_default = "mirror"

} 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

# 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

# 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"

# How much stack (in KB) to reserve for use while devices suspended

104

Sample lvm.conf File

reserved_stack = 256

# How much memory (in KB) to reserve for use while devices suspended

reserved_memory = 8192

# Nice value used while devices suspended

process_priority = -18

# 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 or VG

#

# volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]

# Size (in KB) of each copy operation when mirroring

mirror_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"

# 'mirror_image_fault_policy' and 'mirror_log_fault_policy' define

# how a device failure affecting a mirror 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

# 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. This

# policy acts like "remove" if no suitable device and space can

# be allocated for the replacement.

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

105

Appendix B. The LVM Configuration Files

# 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

# 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/gconv-modules.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 total number of metadata areas available then

# metadata is stored in them all.

# The default value of 0 ("unmanaged") disables this automatic

# management and allows you to control which metadata areas

106

Sample lvm.conf File

# 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"

# Full path of the dmeventd binary.

#

# executable = "/sbin/dmeventd"

}

107

108

Appendix C. 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. Snapshots cannot be tagged.

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. Snapshots cannot be tagged.

The following command lists all the logical volumes with the database tag.

lvs @database

C.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

C.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 hostname. 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 hostname.

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.

109

Appendix C. LVM Object Tags

For example, the following entry in the configuration file always defines tag1, and defines tag2 if the hostname is host1.

tags { tag1 { } tag2 { host_list = ["host1"] } }

C.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.

110

Appendix D. 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.

D.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.

D.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

111

Appendix D. LVM Volume Group Metadata

• A version number which is incremented whenever the metadata gets updated

• 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

D.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" # Linux tng3-1 2.6.18-8.el5 #1 SMP Fri Jan 26 14:15:21 EST

2007 i686 creation_time = 1170196095 # 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 = ["ALLOCATABLE"]

dev_size = 35964301 # 17.1491 Gigabytes

pe_start = 384

pe_count = 4390 # 17.1484 Gigabytes

}

pv1 {

id = "ZHEZJW-MR64-D3QM-Rv7V-Hxsa-zU24-wztY19"

device = "/dev/sdb" # Hint only

112

status = ["ALLOCATABLE"]

dev_size = 35964301 # 17.1491 Gigabytes

pe_start = 384

pe_count = 4390 # 17.1484 Gigabytes

}

pv2 {

id = "wCoG4p-55Ui-9tbp-VTEA-jO6s-RAVx-UREW0G"

device = "/dev/sdc" # Hint only

status = ["ALLOCATABLE"]

dev_size = 35964301 # 17.1491 Gigabytes

pe_start = 384

pe_count = 4390 # 17.1484 Gigabytes

}

pv3 {

id = "hGlUwi-zsBg-39FF-do88-pHxY-8XA2-9WKIiA"

device = "/dev/sdd" # Hint only

status = ["ALLOCATABLE"]

dev_size = 35964301 # 17.1491 Gigabytes

pe_start = 384

pe_count = 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 # 5 Gigabytes

type = "striped"

stripe_count = 1 # linear

stripes = [

"pv0", 0

]

}

segment2 {

start_extent = 1280

extent_count = 1280 # 5 Gigabytes

type = "striped"

stripe_count = 1 # linear

stripes = [

"pv1", 0

]

}

}

}

}

Sample Metadata

113

114

Appendix E. Revision History

Revision 3.0-5 Thu Dec 1 2011

Release for GA of Red Hat Enterprise Linux 6.2

Steven Levine [email protected]

Revision 3.0-4 Mon Nov 21 2011

Resolves: #755371, #755373, #755374

Documentation QE review

Steven Levine [email protected]

Revision 3.0-3 Mon Nov 07 2011

Resolves: #749487

Clarifies pvcreate example for a whole disk.

Steven Levine [email protected]

Revision 3.0-2 Wed Oct 12 2011

Resolves: #744999

Fixes small typographical errors.

Steven Levine [email protected]

Revision 3.0-1 Mon Sep 19 2011 Steven Levine [email protected]

Initial revision for Red Hat Enterprise Linux 6.2 Beta release

Resolves: #730788

Documents support for issuing discards to a logical volume's underlying physical volume space when the physical volume space is no longer in use.

Resolves: #728361

Removes outdated reference to deprecated documentation.

Resolves: #714579

Fixes minor typographical errors.

Resolves: #664107

Corrects documented location of .cache file.

Revision 2.0-1 Thu May 19 2011

Initial release for Red Hat Enterprise Linux 6.1

Steven Levine [email protected]

Resolves: #694619

Documents new cling allocation policy when extending a logical volume.

Resolves: #682649

Adds warning about running multiple mirror creation commands in succession on clustered volumes.

Resolves: #674100

Adds example of output for dmsetup ls --tree command.

Resolves: #694607

115

Appendix E. Revision History

Documents support for including multiple --addtag and --deltag arguments on a single command line.

Resolves: #694604

Documents support for expanded character list in tags.

Resolves: #694611

Documents support for mirrored stripes.

Resolves: #694616

Documents support for snapshots of mirrored volumes.

Resolves: #694618

Documents support for snapshots of exclusively-activated cluster volumes.

Resolves: #682648

Documents that when a mirror leg is re-allocated the mirror log may be moved as well.

Resolves: #661530

Updates example cluster.conf to one that documents current features.

Resolves: #642400

Adds note about cluster log management being maintained by cluster node with lowest cluster ID.

Resolves: #663462

Removes outdated references to Xen virtual machine monitor.

Revision 1.0-1 Wed Nov 10 2010

Initial release for Red Hat Enterprise Linux 6

Steven Levine [email protected]

116

Index

Symbols

/lib/udev/rules.d directory, 93

A activating logical volumes

individual nodes, 49

activating volume groups, 30 individual nodes, 30 local node only, 30

administrative procedures, allocation

policy, 26

preventing, 25

archive file, 18, 31

B backup

file, 18

metadata, 18, 31 backup file, 31

block device

scanning, 23

C cache file

building, 28

cluster environment, 4, 17

CLVM

definition, 4

clvmd daemon, 5

command line units, 21

configuration examples, creating

logical volume, 32

logical volume, example, 59

LVM volumes in a cluster, 17

physical volumes, 22

striped logical volume, example, 60

volume group, clustered, 26

volume groups, 25

creating LVM volumes

overview, 17

D

data relocation, online, 48

deactivating volume groups, 30 exclusive on one node, 30 local node only, 30

device numbers

major, 41 minor, 41 persistent, 41

device path names, 21

device scan filters, 47

device size, maximum, 26 device special file directory, 26

display

sorting output, 57

displaying

logical volumes, 43, 54

physical volumes, 24, 51

volume groups, 27, 53

E extent

allocation, 26 definition, 10, 26

F failed devices

displaying, 69

features, new and changed, 1

feedback

contact information for this manual, viii

file system

growing on a logical volume, 18

filters, 47

G growing file system

logical volume, 18

H

help display, 22

I initializing

partitions, 23 physical volumes, 23

Insufficient Free Extents message, 75

L linear logical volume

converting to mirrored, 39

creation, 32

definition, 11

logging, 19

logical volume

administration, general, 32

changing parameters, 42

creation, 32

creation example, 59

definition, 2, 11

117

Index

displaying, 43, 49, 54

exclusive access, 49

extending, 43 growing, 43

linear, 32

local access, 49

lvs display arguments, 54

mirrored, 34

reducing, 47

removing, 42 renaming, 42 resizing, 42

shrinking, 47

snapshot, 39

striped, 34

lvchange command, 42

lvconvert command, 39

lvcreate command, 32

lvdisplay command, 43 lvextend command, 43

LVM

architecture overview, 3

clustered, 4 components, 4,

custom report format, 49

directory structure, 26

help, 22

history, 3

label, 9

logging, 19

logical volume administration, 32

physical volume administration, 22

physical volume, definition, 9

volume group, definition, 10

LVM1, 3

LVM2, 3

lvmdiskscan command, 23

lvreduce command, 42, 47

lvremove command, 42 lvrename command, 42

lvs command, 49, 54 display arguments, 54

lvscan command, 43

M

man page display, 22

metadata

backup, 18, 31

recovery, 73

mirrored logical volume

clustered, 66

converting to linear, 39

creation, 34

definition, 13

118

failure policy, 37

failure recovery, 70

reconfiguration, 39

mirror_image_fault_policy configuration

parameter, 37

mirror_log_fault_policy configuration parameter,

37

O

online data relocation, 48

overview

features, new and changed, 1

P

partition type, setting, 23

partitions

multiple, 10

path names, 21

persistent device numbers, 41

physical extent

preventing allocation, 25

physical volume

adding to a volume group, 27

administration, general, 22 creating, 22

definition, 9

display, 51

displaying, 24, 49

illustration, 9

initializing, 23

layout, 9

pvs display arguments, 51

recovery, 74

removing, 25

removing from volume group, 29

removing lost volume, 75

resizing, 25

pvdisplay command, 24

pvmove command, 48

pvremove command, 25 pvresize command, 25

pvs command, 49

display arguments, 51

pvscan command, 24

R removing

disk from a logical volume, 63

logical volume, 42

physical volumes, 25

renaming

logical volume, 42

volume group, 31

report format, LVM devices, 49

resizing

logical volume, 42

physical volume, 25

rules.d directory, 93

S scanning

block devices, 23

scanning devices, filters, 47

snapshot logical volume

creation, 39

snapshot volume

definition, 14

striped logical volume

creation, 34

creation example, 60

definition, 12

extending, 44 growing, 44

T troubleshooting,

U

udev device manager, 92

udev rules, 93

units, command line, 21

V

verbose output, 21

vgcfbackup command, 31 vgcfrestore command, 31

vgchange command, 29

vgcreate command, 25, 26

vgdisplay command, 28

vgexport command, 31

vgextend command, 27

vgimport command, 31

vgmerge command, 30

vgmknodes command, 32

vgreduce command, 29

vgrename command, 31

vgs command, 49

display arguments, 53

vgscan command, 28

vgsplit command, 30

volume group

activating, 30

administration, general, 25

changing parameters, 29

combining, 30

creating, 25

creating in a cluster, 26

deactivating, 30

definition, 10

displaying, 27, 49, 53

extending, 27 growing, 27

merging, 30

moving between systems, 31

reducing, 29

removing, 30

renaming, 31

shrinking, 29

splitting, 30

example procedure, 61

vgs display arguments, 53

119

120