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Red Hat Enterprise Linux 4
DM Multipath
DM Multipath Configuration and Administration
Edition 1.0
Landmann
Red Hat Enterprise Linux 4 DM Multipath
DM Multipath Configuration and Administration
Edition 1.0
Landmann
rlandmann@redhat.co m
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Abstract
T his book provides information on using the Device-Mapper Multipath feature of Red Hat Enterprise
Linux 4.
Table of Contents
Table of Contents
.Preface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. . . . . . . . . .
1. Audience
4
2. Related Documentation
4
3. Feedback
4
4. Document Conventions
5
4.1. T ypographic Conventions
5
4.2. Pull-quote Conventions
6
4.3. Notes and Warnings
7
.Chapter
. . . . . . . . 1.
. . .Device
. . . . . . . Mapper
. . . . . . . . .Multipathing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8. . . . . . . . . .
1.1. Overview of DM-Multipath
8
1.2. Storage Array Support
10
1.3. DM-Multipath Components
10
1.4. DM-Multipath Setup Overview
11
.Chapter
. . . . . . . . 2.
. . .Multipath
. . . . . . . . . . Devices
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
............
2.1. Multipath Device Identifiers
12
2.2. Consistent Multipath Device Names in a Cluster
12
2.3. Multipath Device Attributes
13
2.4. Multipath Devices in Logical Volumes
13
.Chapter
. . . . . . . . 3.
. . .Setting
. . . . . . . .Up
. . . DM-Multipath
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
............
3.1. Setting Up DM-Multipath
14
3.2. Ignoring Local Disks when Generating Multipath Devices
15
3.3. Adding Devices to the Multipathing Database
17
.Chapter
........4
. ...T. he
. . . .DM-Multipath
. . . . . . . . . . . . . .Configuration
. . . . . . . . . . . . . . .File
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
............
4.1. Configuration File Overview
18
4.2. Configuration File Blacklist
19
4.2.1. Blacklisting By WWID
19
4.2.2. Blacklisting By Device Name
19
4.3. Configuration File Defaults
20
4.4. Multipaths Device Configuration Attributes
24
4.5. Configuration File Devices
26
.Chapter
. . . . . . . . 5.
. . .DM-Multipath
. . . . . . . . . . . . . . Administration
. . . . . . . . . . . . . . . .and
. . . .T
. .roubleshooting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
...........
5.1. Multipath Command Output
30
5.2. Multipath Queries with multipath Command
31
5.3. Multipath Command Options
31
5.4. Determining Device Mapper Entries with the dmsetup Command
31
5.5. T roubleshooting with the multipathd Interactive Console
32
5.6. Resizing an Online Multipathed Device (RHEL 4.8 and later)
32
. . . . . . . . . .History
Revision
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
............
.Index
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
............
A
34
B
34
C
34
D
35
E
36
F
36
G
36
1
Red Hat Enterprise Linux 4 D M Multipath
H
K
L
M
N
P
R
S
U
V
W
2
36
36
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Table of Contents
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Red Hat Enterprise Linux 4 D M Multipath
Preface
T his book describes the Device Mapper Multipath (DM-Multipath) feature of Red Hat Enterprise Linux.
1. Audience
T his book is intended to be used by system administrators managing systems running the Linux
operating system. It requires familiarity with Red Hat Enterprise Linux.
2. Related Documentation
For more information about using Red Hat Enterprise Linux, refer to the following resources:
Red Hat Enterprise Linux Installation Guide — Provides information regarding installation of Red Hat
Enterprise Linux.
Red Hat Enterprise Linux Introduction to System Administration — Provides introductory information
for new Red Hat Enterprise Linux system administrators.
Red Hat Enterprise Linux System Administration Guide — Provides more detailed information about
configuring Red Hat Enterprise Linux to suit your particular needs as a user.
Red Hat Enterprise Linux Reference Guide — Provides detailed information suited for more
experienced users to reference when needed, as opposed to step-by-step instructions.
Red Hat Enterprise Linux Security Guide — Details the planning and the tools involved in creating a
secured computing environment for the data center, workplace, and home.
For more information about Red Hat Cluster Suite for Red Hat Enterprise Linux, refer to the following
resources:
Red Hat Cluster Suite Overview — Provides a high level overview of the Red Hat Cluster Suite.
Configuring and Managing a Red Hat Cluster — Provides information about installing, configuring and
managing Red Hat Cluster components.
Global File System: Configuration and Administration — Provides information about installing,
configuring, and maintaining Red Hat GFS (Red Hat Global File System).
LVM Administrator's Guide: Configuration and Administration — Provides a description of the Logical
Volume Manager (LVM), including information on running LVM in a clustered environment.
Using GNBD with Global File System — Provides an overview on using Global Network Block Device
(GNBD) with Red Hat GFS.
Linux Virtual Server Administration — Provides information on configuring high-performance systems
and services with the Linux Virtual Server (LVS).
Red Hat Cluster Suite Release Notes — Provides information about the current release of Red Hat
Cluster Suite.
Red Hat Cluster Suite documentation and other Red Hat documents are available in HT ML and PDF
versions online at the following location:
http://www.redhat.com/docs
3. Feedback
If you spot a typo, 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/bugzilla/) against the component rhcs.
4
Preface
Be sure to mention the manual's identifier:
rh-MPIO(EN)-4.9 (2011-02-16T16:48)
By mentioning this manual's identifier, we know exactly which version of the guide you have.
If you have a suggestion for improving the documentation, try to be as specific as possible. If you have
found an error, please include the section number and some of the surrounding text so we can find it
easily.
4. Document Conventions
T his 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 set. T he
Liberation Fonts set is also used in HT ML 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 include the Liberation
Fonts set by default.
4.1. Typographic Conventions
Four typographic conventions are used to call attention to specific words and phrases. T hese
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
keys and key combinations. For example:
T o see the contents of the file m y_next_bestselling_novel in your current working
directory, enter the cat m y_next_bestselling_novel command at the shell prompt
and press Enter to execute the command.
T he above includes a file name, a shell command and a key, all presented in mono-spaced bold and all
distinguishable thanks to context.
Key combinations can be distinguished from an individual key by the plus sign that connects each part of
a key combination. For example:
Press Enter to execute the command.
Press Ctrl+Alt+F2 to switch to a virtual terminal.
T he first example highlights a particular key to press. T he second example highlights a key combination:
a set of three keys 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 m ono-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
T his denotes words or phrases encountered on a system, including application names; dialog box text;
5
Red Hat Enterprise Linux 4 D M Multipath
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, select the Left-handed m ouse 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).
T o 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. T he character you sought will be highlighted in the Character T able. Double-click
this highlighted character to place it in the T ext to copy field and then click the Copy
button. Now switch back to your document and choose Edit → Paste from the gedit menu
bar.
T he 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:
T o connect to a remote machine using ssh, type ssh username@ domain.name at a shell
prompt. If the remote machine is exam ple.com and your username on that machine is
john, type ssh john@ exam ple.com .
T he m ount -o rem ount file-system command remounts the named file system. For
example, to remount the /hom e file system, the command is m ount -o rem ount /hom e.
T o 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:
Publican is a DocBook publishing system.
4.2. Pull-quote Conventions
T erminal output and source code listings are set off visually from the surrounding text.
Output sent to a terminal is set in m ono-spaced rom an and presented thus:
books
books_tests
Desktop
Desktop1
documentation
downloads
drafts
images
mss
notes
photos
scripts
stuff
svgs
svn
Source-code listings are also set in m ono-spaced rom an but add syntax highlighting as follows:
6
Preface
static int kvm_vm_ioctl_deassign_device(struct kvm *kvm,
struct kvm_assigned_pci_dev *assigned_dev)
{
int r = 0;
struct kvm_assigned_dev_kernel *match;
mutex_lock(&kvm->lock);
match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
assigned_dev->assigned_dev_id);
if (!match) {
printk(KERN_INFO "%s: device hasn't been assigned before, "
"so cannot be deassigned\n", __func__);
r = -EINVAL;
goto out;
}
kvm_deassign_device(kvm, match);
kvm_free_assigned_device(kvm, match);
out:
mutex_unlock(&kvm->lock);
return r;
}
4.3. 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.
Warning
Warnings should not be ignored. Ignoring warnings will most likely cause data loss.
7
Red Hat Enterprise Linux 4 D M Multipath
Chapter 1. Device Mapper Multipathing
Device Mapper Multipathing (DM-Multipath) allows you to configure multiple I/O paths between server
nodes and storage arrays into a single device. T hese I/O paths are physical SAN connections that can
include separate cables, switches, and controllers. Multipathing aggregates the I/O paths, creating a new
device that consists of the aggregated paths.
1.1. Overview of DM-Multipath
DM-Multipath can be used to provide:
Redundancy
DM-Multipath can provide failover in an active/passive configuration. In an active/passive
configuration, only half the paths are used at any time for I/O. If any element of an I/O path (the cable,
switch, or controller) fails, DM-Multipath switches to an alternate path.
Improved Performance
DM-Multipath can be configured in active/active mode, where I/O is spread over the paths in a roundrobin fashion. In some configurations, DM-Multipath can detect loading on the I/O paths and
dynamically re-balance the load.
Figure 1.1, “Active/Passive Multipath Configuration with One RAID Device” shows an active/passive
configuration with two I/O paths from the server to a RAID device. T here are 2 HBAs on the server, 2
SAN switches, and 2 RAID controllers.
Figure 1.1. Active/Passive Multipath Configuration with One RAID Device
In this configuration, there is one I/O path that goes through hba1, SAN1, and controller 1 and a second
I/O path that goes through hba2, SAN2, and controller2. T here are many points of possible failure in this
configuration:
HBA failure
FC cable failure
SAN switch failure
8
Chapter 1. D evice Mapper Multipathing
Array controller port failure
With DM-Multipath configured, a failure at any of these points will cause DM-Multipath to switch to the
alternate I/O path.
Figure 1.2, “Active/Passive Multipath Configuration with T wo RAID Devices” shows a more complex
active/passive configuration with 2 HBAs on the server, 2 SAN switches, and 2 RAID devices with 2 RAID
controllers each.
Figure 1.2. Active/Passive Multipath Configuration with T wo RAID Devices
As in the example shown in Figure 1.1, “Active/Passive Multipath Configuration with One RAID Device”,
there are two I/O paths to each RAID device. With DM-Multipath configured, a failure at any of the points
of the I/O path to either of the RAID devices will cause DM-Multipath to switch to the alternate I/O path for
that device.
Figure 1.3, “Active/Active Multipath Configuration with One RAID Device” shows an active/active
configuration with 2 HBAs on the server, 1 SAN switch, and 2 RAID controllers. T here are four I/O paths
from the server to a storage device:
hba1 to controller1
hba1 to controller2
hba2 to controller1
hba2 to controller2
In this configuration, I/O can be spread among those four paths.
9
Red Hat Enterprise Linux 4 D M Multipath
Figure 1.3. Active/Active Multipath Configuration with One RAID Device
1.2. Storage Array Support
By default, DM-Multipath includes support for the most common storage arrays that support DMMultipath. T he supported devices can be found in the m ultipath.conf.defaults file. If your storage
array supports DM-Multipath and is not configured by default in this file, you may need to add them to the
DM-Multipath configuration file, m ultipath.conf. For information on the DM-Multipath configuration
file, see Chapter 4, The DM-Multipath Configuration File.
Some storage arrays require special handling of I/O errors and path switching. T hese require separate
hardware handler kernel modules.
1.3. DM-Multipath Components
T able 1.1, “DM-Multipath Components”. describes the components of DM-Multipath.
10
Chapter 1. D evice Mapper Multipathing
T able 1.1. DM-Multipath Components
Component
Description
dm -m ultipath kernel module
Reroutes I/O and supports failover for paths and path groups.
m ultipath command
Lists and configures multipath devices. Normally started up with
/etc/rc.sysinit, it can also be started up by a udev program
whenever a block device is added or it can be run by the
initram fs file system.
m ultipathd daemon
Monitors paths; as paths fail and come back, it may initiate path
group switches. Provides for interactive changes to multipath
devices. T his must be restarted for any changes to the
/etc/m ultipath.conf file.
kpartx command
Creates device mapper devices for the partitions on a device It is
necessary to use this command for DOS-based partitions with DMMP. T he kpartx is provided in its own package, but the devicem apper-m ultipath package depends on it.
1.4. DM-Multipath Setup Overview
DM-Multipath includes compiled-in default settings that are suitable for common multipath configurations.
Setting up DM-multipath is often a simple procedure.
T he basic procedure for configuring your system with DM-Multipath is as follows:
1. Install device-m apper-m ultipath rpm.
2. Edit the m ultipath.conf configuration file:
comment out the default blacklist
change any of the existing defaults as needed
save the configuration file
3. Start the multipath daemons.
4. Create the multipath device with the m ultipath command.
Detailed setup instructions for several example multipath configurations are provided in see Chapter 3,
Setting Up DM-Multipath.
11
Red Hat Enterprise Linux 4 D M Multipath
Chapter 2. Multipath Devices
Without DM-Multipath, each path from a server node to a storage controller is treated by the system as a
separate device, even when the I/O path connects the same server node to the same storage controller.
DM-Multipath provides a way of organizing the I/O paths logically, by creating a single multipath device
on top of the underlying devices.
2.1. Multipath Device Identifiers
Each multipath device has a World Wide Identifier (WWID), which is guaranteed to be globally unique and
unchanging. By default, the name of a multipath device is set to its WWID. Alternately, you can set the
user_friendly_nam es option in the multipath configuration file, which sets the alias to a node-unique
name of the form m pathn.
For example, a node with two HBAs attached to a storage controller with two ports via a single unzoned
FC switch sees four devices: /dev/sda, /dev/sdb, dev/sdc, and /dev/sdd. DM-Multipath creates a
single device with a unique WWID that reroutes I/O to those four underlying devices according to the
multipath configuration. When the user_friendly_nam es configuration option is set to yes, the name
of the multipath device is set to m pathn.
When new devices are brought under the control of DM-Multipath, the new devices may be seen in three
different places under the /dev directory: /dev/m apper/m pathn, /dev/m path/m pathn, and
/dev/dm -n.
T he devices in /dev/m apper are created early in the boot process. Use these devices to access
the multipathed devices, for example when creating logical volumes.
T he devices in /dev/m path are provided as a convenience so that all multipathed devices can be
seen in one directory. T hese devices are created by the udev device manager and may not be
available on startup when the system needs to access them. Do not use these devices for creating
logical volumes or filesystems.
Any devices of the form /dev/dm -n are for internal use only and should never be used.
For information on the multipath configuration defaults, including the user_friendly_nam es
configuration option, see see Section 4.3, “Configuration File Defaults”.
You can also set the name of a multipath device to a name of your choosing by using the alias option
in the m ultipaths section of the multipath configuration file. For information on the m ultipaths
section of the multipath configuration file, see see Section 4.4, “Multipaths Device Configuration
Attributes”.
2.2. Consistent Multipath Device Names in a Cluster
When the user_friendly_nam es configuration option is set to yes, the name of the multipath device
is unique to a node, but it is not guaranteed to be the same on all nodes using the multipath device. T his
should not cause any difficulties if you use LVM to create logical devices from the multipath device, but if
you require that your multipath device names be consistent in every node in the cluster you perform one
of the following procedures:
Use the alias option in the m ultipaths section of the multipath configuration file to set the name
of the multipath device. T he alias for the multipath device is consistent across all the nodes in a
cluster. For information on the m ultipaths section of the multipath configuration file, see see
Section 4.4, “Multipaths Device Configuration Attributes”.
If you want the system-defined user-friendly names to be consistent across all nodes in the cluster,
12
Chapter 2. Multipath D evices
If you want the system-defined user-friendly names to be consistent across all nodes in the cluster,
set up all of the multipath devices on one machine. T hen copy the bindings file from that machine
to all the other machines in the cluster. T he bindings file is located at
/var/lib/m ultipath/bindings by default, but as of RHEL 4.6 and later you can set this value
to a different location with the bindings_file parameter of the defaults section of the
configuration file.
2.3. Multipath Device Attributes
In addition to the user_friendly_nam es and alias options, a multipath device has numerous
attributes. You can modify these attributes for a specific multipath device by creating an entry for that
device in the m ultipaths section of the multipath configuration file. For information on the
m ultipaths section of the multipath configuration file, see see Section 4.4, “Multipaths Device
Configuration Attributes”.
2.4. Multipath Devices in Logical Volumes
After creating multipath devices, you can use the multipath device names just as you would use a
physical device name when creating an LVM physical volume. For example, if /dev/m apper/m path0 is
the name of a multipath device, the following command will mark /dev/m apper/m path0 as a physical
volume.
pvcreate /dev/mapper/mpath0
You can use the resulting LVM physical device when you create an LVM volume group just as you would
use any other LVM physical device.
When you create an LVM logical volume that uses active/passive multipath arrays as the underlying
physical devices, you should include filters in the lvm .conf file to exclude the disks that underlie the
multipath devices. T his is because if the array automatically changes the active path to the passive path
when it receives I/O, multipath will failover and failback whenever LVM scans the passive path if these
devices are not filtered. For active/passive arrays that require a command to make the passive path
active, LVM prints a warning message when this occurs.
T o filter all SCSI devices in the multipath configuration file (lvm .conf), include the following filter in the
devices section of the file.
filter = [ "r/disk/", "r/sd.*/", "a/.*/" ]
13
Red Hat Enterprise Linux 4 D M Multipath
Chapter 3. Setting Up DM-Multipath
T his chapter provides step-by-step example procedures for configuring DM-Multipath. It includes the
following procedures:
Basic DM-Multipath setup
Ignoring local disks
Adding more devices to the configuration file
3.1. Setting Up DM-Multipath
Before setting up DM-Multipath on your system, ensure that your system has been updated and
includes the device-m apper-m ultipath package.
Use the following procedure to set up DM-Multipath for a basic failover configuration.
1. Edit the /etc/m ultipath.conf file by commenting out the following lines at the top of the file.
T his section of the configuration file, in its initial state, blacklists all devices. You must comment it
out to enable multipathing.
devnode_blacklist {
devnode "*"
}
After commenting out those lines, this section appears as follows.
# devnode_blacklist {
#
devnode "*"
# }
2. T he default settings for DM-Multipath are compiled in to the system and do not need to be
explicitly set in the /etc/m ultipath.conf file.
T he default value of path_grouping_policy is set to failover, so in this example you do
not need to change the default value. For information on changing the values in the configuration
file to something other than the defaults, see Chapter 4, The DM-Multipath Configuration File.
T he initial defaults section of the configuration file configures your system that the names of the
multipath devices are are of the form m pathn; without this setting, the names of the multipath
devices would be aliased to the WWID of the device.
3. Save the configuration file and exit the editor.
4. Execute the following commands:
modprobe dm-multipath
service multipathd start
multipath -v2
T he m ultipath -v2 command prints out multipathed paths that show which devices are
multipathed, but only for the devices created by this command. If the command does yield any
output, you can check your multipath devices as follows:
Run the m ultipath -ll command. T his lists all the multipath devices.
If running the m ultipath -ll command does not show the device, verify that multipath is
configured properly by checking the /etc/m ultipath file and making sure that the SCSI
devices you want to be multipathed exist on the system.
14
Chapter 3. Setting Up D M-Multipath
If the SCSI devices do not appear, ensure that all SAN connections are set up properly.
For further information on the m ultipath command and its output, see Section 5.1, “Multipath
Command Output”, see Section 5.2, “Multipath Queries with multipath Command”, and see
Section 5.3, “Multipath Command Options”.
5. Execute the following command to ensure sure that the multipath daemon starts on bootup:
chkconfig multipathd on
Since the value of user_friendly_nam e is set to yes in the configuration filea the multipath devices
will be created as /dev/m apper/m pathn. For information on setting the name of the device to an alias
of your choosing, see Chapter 4, The DM-Multipath Configuration File.
3.2. Ignoring Local Disks when Generating Multipath Devices
Some machines have local SCSI cards for their internal disks. DM-Multipath is not recommended for
these devices. T he following procedure shows how to modify the multipath configuration file to ignore the
local disks when configuring multipath.
1. Determine which disks are the internal disks and mark them as the ones to blacklist.
In this example, /dev/sda is the internal disk. Note that as originally configured in the default
multipath configuration file, executing the m ultipath -v2 shows the local disk, /dev/sda, in the
multipath map.
For further information on the m ultipath command output, see Section 5.1, “Multipath Command
Output”.
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Red Hat Enterprise Linux 4 D M Multipath
[root@rh4cluster1 ~]# multipath -v2
create: SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
[size=33 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 0:0:0:0 sda 8:0
[--------device-mapper ioctl cmd 9 failed: Invalid argument
device-mapper ioctl cmd 14 failed: No such device or address
create: 3600a0b80001327d80000006d43621677
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:0 sdb 8:16
\_ 3:0:0:0 sdf 8:80
create: 3600a0b80001327510000009a436215ec
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:1 sdc 8:32
\_ 3:0:0:1 sdg 8:96
create: 3600a0b80001327d800000070436216b3
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:2 sdd 8:48
\_ 3:0:0:2 sdh 8:112
create: 3600a0b80001327510000009b4362163e
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:3 sde 8:64
\_ 3:0:0:3 sdi 8:128
2. In order to prevent the device mapper from mapping /dev/sda in its multipath maps, edit the
devnode_blacklist section of the /etc/m ultipath.conf file to include this device.
Although you could blacklist the sda device using a devnode type, that would not be safe
procedure since /dev/sda is not guaranteed to be the same on reboot. T o blacklist individual
devices, you can blacklist using the WWID of that device.
Note that in the output to the m ultipath -vs command, the WWID of the /dev/sda device is
SIBM-ESXSST 336732LC____F3ET 0EP0Q000072428BX1. T o blacklist this device, include the
following in the /etc/m ultipath.conf file.
devnode_blacklist {
wwid SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
}
3. Run the following commands:
multipath -F
multipath -v2
T he local disk or disks should no longer be listed in the new multipath maps, as shown in the
following example.
16
Chapter 3. Setting Up D M-Multipath
[root@rh4cluster1 ~]# multipath -F
[root@rh4cluster1 ~]# multipath -v2
create: 3600a0b80001327d80000006d43621677
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:0 sdb 8:16
\_ 3:0:0:0 sdf 8:80
create: 3600a0b80001327510000009a436215ec
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:1 sdc 8:32
\_ 3:0:0:1 sdg 8:96
create: 3600a0b80001327d800000070436216b3
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:2 sdd 8:48
\_ 3:0:0:2 sdh 8:112
create: 3600a0b80001327510000009b4362163e
[size=12 GB][features="0"][hwhandler="0"]
\_ round-robin 0
\_ 2:0:0:3 sde 8:64
\_ 3:0:0:3 sdi 8:128
3.3. Adding Devices to the Multipathing Database
By default, DM-Multipath includes support for the most common storage arrays that support DMMultipath. T he default configuration values, including supported devices, can be found in the
m ultipath.conf.defaults file.
If you need to add a storage device that is not supported by default as a known multipath device, edit the
/etc/m ultipath.conf file and insert the appropriate device information.
For example, to add information about the HP Open-V series the entry looks like this:
devices {
device {
vendor "HP"
product "OPEN-V."
getuid_callout "/sbin/scsi_id -g -u -p0x80 -s /block/%n"
}
}
For more information on the devices section of the configuration file, see Section 4.5, “Configuration
File Devices”.
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Red Hat Enterprise Linux 4 D M Multipath
Chapter 4. The DM-Multipath Configuration File
By default, DM-Multipath provides configuration values for the most common uses of multipathing. In
addition, DM-Multipath includes support for the most common storage arrays that support DM-Multipath.
T he default configuration values and the supported devices can be found in the
/usr/share/doc/device-m apper-m ultipath-0.4 .5/m ultipath.conf.defaults file.
Note
T he location and contents of the m ultipath.conf.defaults file may differ slightly from the
example shown in this chapter depending on the release of RHEL 4 that you are running.
You can override the default configuration values for DM-Multipath by editing the
/etc/m ultipath.conf configuration file. If necessary, you can also add a storage array that is not
supported by default to the configuration file. T his chapter provides information on parsing and modifying
the m ultipath.conf file. It contains sections on the following topics:
Configuration file overview
Configuration file blacklist
Configuration file defaults
Configuration file multipaths
Configuration file devices
In the multipath configuration file, you need to specify only the sections that you need for your
configuration, or that you wish to change from the default values specified in the
m ultipath.conf.defaults file. If there are sections of the file that are not relevant to your
environment or for which you do not need to override the default values, you can leave them commented
out, as they are in the initial file.
T he configuration file allows regular expression description syntax.
An annotated version of the configuration file can be found in /usr/share/doc/device-m apperm ultipathd-0.4 .5/m ultipath.conf.annotated.
4.1. Configuration File Overview
T he multipath configuration file is divided into the following sections:
devnode_blacklist
Listing of specific devices that will not be considered for multipath. By default all devices are
blacklisted. Usually the default devnode_blacklist section is commented out.
defaults
General default settings for DM-Multipath.
multipaths
Settings for the characteristics of individual multipath devices. T hese values overwrite what is
specified in the defaults and devices sections of the configuration file.
18
Chapter 4. The D M-Multipath Configuration File
devices
Settings for the individual storage controllers. T hese values overwrite what is specified in the
defaults section of the configuration file. If you are using a storage array that is not
supported by default, you may need to create a devices subsection for your array.
When the system determines the attributes of a multipath device, first it checks the multipath settings,
then the per devices settings, then the multipath system defaults.
4.2. Configuration File Blacklist
T he devnode_blacklist section of the multipath configuration file specifies the devices that will not
be used when the system configures multipath devices. Devices that are blacklisted will not be grouped
into a multipath device.
By default, all devices are blacklisted, since the following lines appear in the initial configuration file.
devnode_blacklist {
devnode "*"
}
T o enable multipathing on all of the devices that are supported by default, comment out those lines, as
described in Section 3.1, “Setting Up DM-Multipath”.
After commenting out the universal blacklist, you can specify general device types and individual devices
to blacklist. You can blacklist devices according to the following criteria:
By WWID, as described in Section 4.2.1, “Blacklisting By WWID”
By device name, as described in Section 4.2.2, “Blacklisting By Device Name”
By default, a variety of device types are blacklisted, even after you comment out the initial
devnode_blacklist section of the configuration file. For information, see Section 4.2.2, “Blacklisting
By Device Name”.
4.2.1. Blacklisting By WWID
You can specify individual devices to blacklist by their World-Wide IDentification with a wwid entry in the
blacklist section of the configuration file.
T he following example shows the lines in the configuration file that would blacklist a device with a WWID
of 26353900f02796769.
blacklist {
wwid 26353900f02796769
}
4.2.2. Blacklisting By Device Name
You can blacklist device types by device name so that they will not be grouped into a multipath device by
specifying a devnode entry in the devnode_blacklist section of the configuration file.
T he following example shows the lines in the configuration file that would blacklist all SCSI devices, since
it blacklists all sd* devices.
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Red Hat Enterprise Linux 4 D M Multipath
devnode_blacklist {
devnode "^sd[a-z]"
}
You can use a devnode entry in the blacklist section of the configuration file to specify individual
devices to blacklist rather than all devices of specific type; this is not recommended, however. Unless it
is statically mapped by udev rules, there is no guarantee that a specific device will have the same name
on reboot. For example, a device name could change from /dev/sda to /dev/sdb on reboot.
By default, the following devnode entries are compiled in the default blacklist; the devices that these
entries blacklist do not generally support DM-Multipath.
blacklist {
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^hd[a-z]"
devnode "^cciss!c[0-9]d[0-9]*"
}
4.3. Configuration File Defaults
T he /etc/m ultipath.conf configuration file includes a defaults section that sets the
user_friendly_nam es parameter to yes, as follows.
defaults {
user_friendly_names yes
}
T his overwrites the default value of the user_friendly_nam es parameter.
T he configuration file includes a template of configuration defaults. T his section is commented out, as
follows.
#defaults {
#
udev_dir
#
polling_interval
#
selector
#
path_grouping_policy
#
getuid_callout
#
prio_callout
#
path_checker
#
rr_min_io
#
rr_weight
#
failback
#
no_path_retry
#
user_friendly_name
#}
/dev
10
"round-robin 0"
multibus
"/sbin/scsi_id -g -u -s /block/%n"
/bin/true
readsector0
100
priorities
immediate
fail
yes
T o overwrite the default value for any of the configuration parameters, you can copy the relevant line
from this template into the defaults section and uncomment it. For example, to overwrite the
path_grouping_policy parameter so that it is m ultibus rather than the default value of
failover, copy the appropriate line from the template to the initial defaults section of the
configuration file, and uncomment it, as follows.
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Chapter 4. The D M-Multipath Configuration File
defaults {
user_friendly_names
path_grouping_policy
}
yes
multibus
T able 4.1, “Multipath Configuration Defaults” describes the attributes that are set in the defaults
section of the m ultipath.conf configuration file. T hese values are used by DM-Multipath unless they
are overwritten by the attributes specified in the devices and m ultipaths sections of the
m ultipath.conf file.
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Red Hat Enterprise Linux 4 D M Multipath
T able 4 .1. Multipath Configuration Defaults
Attribute
Description
udev_dir
Specifies the directory where udev device nodes are created. T he
default value is /udev.
polling_interval
Specifies the interval between two path checks in seconds. T he
default value is 5.
selector
Specifies the default algorithm to use in determining what path to
use for the next I/O operation. T he default value is round-robin
0.
path_grouping_policy
Specifies the default path grouping policy to apply to unspecified
multipaths. Possible values include:
failover = 1 path per priority group
m ultibus = all valid paths in 1 priority group
group_by_serial = 1 priority group per detected serial number
group_by_prio = 1 priority group per path priority value
group_by_node_nam e = 1 priority group per target node name
T he default value is failover.
getuid_callout
Specifies the default program and arguments to call out to obtain a
unique path identifier. An absolute path is required.
T he default value is /sbin/scsi_id -g -u -s.
prio_callout
Specifies the default program and arguments to call out to obtain a
path priority value. For example, the ALUA bits in SPC-3 provide an
exploitable prio value for example. "none" is a valid value. T he
default value is no callout, indicating all paths are equal
features
Specifies the default extra features of multipath devices. T he only
existing feature is queue_if_no_path. T he default value is (null).
path_checker
failback
Specifies the default method used to determine the state of the
paths. Possible values include: readsector0, tur,
em c_clariion, hp_sw, and directio. T he default value is
readsector0.
Specifies path group failback.
A value of 0 or im m ediate specifies that as soon as there is a
path group with a higher priority than the current path group the
system switches to that path group.
A numeric value greater than zero specifies deferred failback,
expressed in seconds.
A value of m anual specifies that failback can happen only with
operator intervention.
T he default value is m anual.
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Chapter 4. The D M-Multipath Configuration File
rr_m in_io
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group. T he default
value is 1000.
m ax_fds
(RHEL 4.7 and later) Sets the maximum number of open file
descriptors for the m ultipathd process. A value of m ax sets the
number of open file descriptors to the system maximum.
rr_weight
If set to priorities, then instead of sending rr_m in_io
requests to a path before calling selector to choose the next
path, the number of requests to send is determined by rr_m in_io
times the path's priority, as determined by the prio_callout
program. Currently, there are priority callouts only for devices that
use the group_by_prio path grouping policy, which means that
all the paths in a path group will always have the same priority.
If set to uniform , all path weights are equal. T he default value is
uniform .
no_path_retry
A numeric value for this attribute specifies the number of times the
system should attempt to use a failed path before disabling
queueing.
A value of fail indicates immediate failure, without queuing.
A value of queue indicates that queuing should not stop until the
path is fixed.
T he default value is (null).
flush_on_last_del
(RHEL 4.7 and later) If set to yes, the m ultipathd daemon will
disable queueing when the last path to a device has been deleted.
T he default value is no.
user_friendly_nam es
If set to yes, specifies that the system should using the bindings
file /var/lib/m ultipath/bindings to assign a persistent and
unique alias to the multipath, in the form of m pathn. If set to no,
specifies that the system should use use the WWID as the alias for
the multipath. In either case, what is specified here will be
overridden by any device-specific aliases you specify in the
m ultipaths section of the configuration file. T he default value is
no.
bindings_file
(RHEL 4.6 and later) T he location of the bindings file that is used
with the user_friendly_nam es option. T he default value is
/var/lib/m ultipath/bindings.
m ode
(RHEL 4.7 and later) T he mode to use for the multipath device
nodes, in octal. T he default value is determined by the process.
uid
(RHEL 4.7 and later) T he user ID to use for the multipath device
nodes. You must use the numeric user ID. T he default value is
determined by the process.
gid
(RHEL 4.7 and later) T he group ID to use for the multipath device
nodes. You must use the numeric group ID. T he default value is
determined by the process.
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Red Hat Enterprise Linux 4 D M Multipath
4.4. Multipaths Device Configuration Attributes
T able 4.2, “Multipath Attributes” shows the attributes that you can set in the m ultipaths section of the
m ultipath.conf configuration file for each specific multipath device. T hese attributes apply only to
the one specified multipath. T hese defaults are used by DM-Multipath and override attributes set in the
defaults and devices sections of the m ultipath.conf file.
24
Chapter 4. The D M-Multipath Configuration File
T able 4 .2. Multipath Attributes
Attribute
Description
wwid
Specifies the WWID of the multipath device to which the
m ultipath attributes apply.
alias
Specifies the symbolic name for the multipath device to which the
m ultipath attributes apply.
path_grouping_policy
Specifies the default path grouping policy to apply to unspecified
multipaths. Possible values include:
failover = 1 path per priority group
m ultibus = all valid paths in 1 priority group
group_by_serial = 1 priority group per detected serial number
group_by_prio = 1 priority group per path priority value
group_by_node_nam e = 1 priority group per target node name
path_selector
Specifies the default algorithm to use in determining what path to
use for the next I/O operation.
rr_m in_io
(RHEL 4.8 and later) Specifies the number of I/O requests to route
to a path before switching to the next path in the current path
group.
failback
Specifies path group failback.
A value of 0 or im m ediate specifies that as soon as there is a
path group with a higher priority than the current path group the
system switches to that path group.
A numeric value greater than zero specifies deferred failback,
expressed in seconds.
A value of m anual specifies that failback can happen only with
operator intervention.
rr_weight
If set to priorities, then instead of sending rr_m in_io
requests to a path before calling selector to choose the next
path, the number of requests to send is determined by rr_m in_io
times the path's priority, as determined by the prio_callout
program. Currently, there are priority callouts only for devices that
use the group_by_prio path grouping policy, which means that
all the paths in a path group will always have the same priority.
If set to uniform , all path weights are equal.
no_path_retry
A numeric value for this attribute specifies the number of times the
system should attempt to use a failed path before disabling
queueing.
A value of fail indicates immediate failure, without queueing.
A value of queue indicates that queuing should not stop until the
path is fixed.
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Red Hat Enterprise Linux 4 D M Multipath
flush_on_last_del
(RHEL 4.7 and later) If set to yes, the m ultipathd daemon will
disable queueing when the last path to a device has been deleted.
T he default value is no.
m ode
(RHEL 4.7 and later) T he mode to use for the multipath device
nodes, in octal. T he default value is determined by the process.
uid
(RHEL 4.7 and later) T he user ID to use for the multipath device
nodes. You must use the numeric user ID. T he default value is
determined by the process.
gid
(RHEL 4.7 and later) T he group ID to use for the multipath device
nodes. You must use the numeric group ID. T he default value is
determined by the process.
T he following example shows multipath attributes specified in the configuration file for two specific
multipath devices. T he first device has a WWID of 3600508b4 000156d70001200000b0000 and a
symbolic name of yellow.
T he second multipath device in the example has a WWID of 1DEC_____3218167584 74 and a
symbolic name of red. In this example, the rr_weight attributes is set to priorities.
multipaths {
multipath {
wwid
alias
path_grouping_policy
path_checker
path_selector
failback
rr_weight
no_path_retry
}
multipath {
wwid
alias
rr_weight
}
}
3600508b4000156d70001200000b0000
yellow
multibus
readsector0
"round-robin 0"
manual
priorities
5
1DEC_____321816758474
red
priorities
4.5. Configuration File Devices
T able 4.3, “Device Attributes” shows the attributes that you can set for each individual storage device in
the devices section of the m ultipath.conf configuration file. T hese attributes are used by DMMultipath unless they are overwritten by the attributes specified in the m ultipaths section of the
m ultipath.conf file for paths that contain the device. T hese attributes override the attributes set in
the defaults section of the m ultipath.conf file.
Many devices that support multipathing are included by default in a multipath configuration. T he values
for the devices that are supported by default are listed in the m ultipath.conf.defaults file. You
probably will not need to modify the values for these devices, but if you do you can overwrite the default
values by including an entry in the the configuration file for the device that overwrites those values. You
can copy the device configuration defaults from the m ultipath.conf.defaults file for the device
and override the values that you want to change.
T o add a device to this section of the configuration file that is not configured automatically by default, you
26
Chapter 4. The D M-Multipath Configuration File
need to set the vendor and product parameters. You can find these values by looking at
/sys/block/device_name/device/vendor and /sys/block/device_name/device/m odel
where device_name is the device to be multipathed, as in the following example:
[root@cypher-06 ~]# cat /sys/block/sda/device/vendor
WINSYS
[root@cypher-06 ~]# cat /sys/block/sda/device/model
SF2372
T he additional parameters to specify depend on your specific device. If the device is active/active, you
will usually not need to set additional parameters. You may want to set path_grouping_policy to
m ultibus. Other parameters you may need to set are no_path_retry and rr_m in_io, as
described in T able 4.3, “Device Attributes”.
If the device is active/passive, but it automatically switches paths with I/O to the passive path, you need
to change the checker function to one that does not send I/O to the path to test if it is working
(otherwise, your device will keep failing over). T his almost always means that you set the
path_checker to tur; this works for all SCSI devices that support the T est Unit Ready command,
which most do.
If the device needs a special command to switch paths, then configuring this device for multipath
requires a hardware handler kernel module. T he current hardware handlers are em c and "rdac. If
these are not sufficient for your device, you may not be able to configure the device for multipath.
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Red Hat Enterprise Linux 4 D M Multipath
T able 4 .3. Device Attributes
Attribute
Description
vendor
Specifies the vendor name of the storage device to which the
device attributes apply, for example COMPAQ.
product
Specifies the product name of the storage device to which the
device attributes apply, for example HSV110 (C)COMPAQ.
bl_product
Specifies a regular expression used to blacklist devices by
vendor/product. Note that for a device to get blacklisted, the
vendor, product, and bl_product strings must all match.
path_grouping_policy
Specifies the default path grouping policy to apply to unspecified
multipaths. Possible values include:
failover = 1 path per priority group
m ultibus = all valid paths in 1 priority group
group_by_serial = 1 priority group per detected serial number
group_by_prio = 1 priority group per path priority value
group_by_node_nam e = 1 priority group per target node name
getuid_callout
Specifies the default program and arguments to call out to obtain a
unique path identifier. An absolute path is required.
prio_callout
Specifies the default program and arguments to call out to obtain a
path weight. Weights are summed for each path group to determine
the next path group to use in case of failure. "none" is a valid value.
path_checker
Specifies the default method used to determine the state of the
paths. Possible values include readsector0 and tur,
em c_clariion, hp_sw, and directio.
path_selector
Specifies the default algorithm to use in determining what path to
use for the next I/O operation.
failback
Specifies path group failback.
A value of 0 or im m ediate specifies that as soon as there is a
path group with a higher priority than the current path group the
system switches to that path group.
A numeric value greater than zero specifies deferred failback,
expressed in seconds.
A value of m anual specifies that failback can happen only with
operator intervention.
features
T he extra features of multipath devices. T he only existing feature is
queue_if_no_path, which is the same as setting
no_path_retry to queue.
hardware_handler
Specifies a module that will be used to perform hardware specific
actions when switching path groups or handling I/O errors. Possible
values include 0, 1 em c, and 1 rdac. T he default value is 0.
rr_m in_io
(RHEL 4.8 and later) Specifies the number of I/O requests to route
to a path before switching to the next path in the current path
28
Chapter 4. The D M-Multipath Configuration File
group. T he default value is 1000.
rr_weight
If set to priorities, then instead of sending rr_m in_io
requests to a path before calling selector to choose the next
path, the number of requests to send is determined by rr_m in_io
times the path's priority, as determined by the prio_callout
program. Currently, there are priority callouts only for devices that
use the group_by_prio path grouping policy, which means that
all the paths in a path group will always have the same priority.
If set to uniform , all path weights are equal. T he default value is
uniform .
no_path_retry
A numeric value for this attribute specifies the number of times the
system should attempt to use a failed path before disabling
queueing.
A value of fail indicates immediate failure, without queuing.
A value of queue indicates that queuing should not stop until the
path is fixed.
T he default value is (null).
flush_on_last_del
(RHEL 4.7 and later) If set to yes, the m ultipathd daemon will
disable queueing when the last path to a device has been deleted.
T he default value is no.
T he following example shows a device entry in the multipath configuration file.
# }
# device {
# vendor
"COMPAQ "
# product
"MSA1000
"
# path_grouping_policy multibus
# path_checker tur
# rr_weight priorities
# }
#}
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Red Hat Enterprise Linux 4 D M Multipath
Chapter 5. DM-Multipath Administration and Troubleshooting
T his chapter will provide information on administering DM-Multipath on a running system. It includes
sections on the following topics:
Multipath Command Output
Multipath Queries with multipath Command
Multipath Command Options
Multipath Queries with dmsetup Command
T roubleshooting with the multipathd Interactive Console
Resizing an Online Multipathed Device
5.1. Multipath Command Output
When you create, modify, or list a multipath device, you get a printout of the current device setup. T he
format is as follows.
For each multipath device:
action_if_any: alias (wwid_if_different_from_alias)
[size][features][hardware_handler]
For each path group:
\_ scheduling_policy [path_group_priority_if_known]
[path_group_status_if_known]
For each path:
\_ host:channel:id:lun devnode major:minor [path_status] [dm_status_if_known]
For example, the output of a multipath command might appear as follows:
mpath1 (3600d0230003228bc000339414edb8101) [size=10
GB][features="0"][hwhandler="0"]
\_ round-robin 0 [prio=1][active]
\_ 2:0:0:6 sdb 8:16 [active][ready]
\_ round-robin 0 [prio=1][enabled]
\_ 3:0:0:6 sdc 8:64 [active][ready]
If the path is up and ready for I/O, the status of the path is ready or active. If the path is down, the
status is faulty or failed. T he path status is updated periodically by the m ultipathd daemon
based on the polling interval defined in the /etc/m ultipath.conf file.
T he dm status is similar to the path status, but from the kernel's point of view. T he dm status has two
states: failed, which is analogous to faulty, and active which covers all other path states.
Occasionally, the path state and the dm state of a device will temporarily not agree.
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Chapter 5. D M-Multipath Administration and Troubleshooting
Note
When a multipath device is being created or modified, the path group status and the dm status
are not known. Also, the features are not always correct. When a multipath device is being listed,
the path group priority is not known.
5.2. Multipath Queries with multipath Command
You can use the -l and -ll options of the m ultipath command to display the current multipath
configuration. T he -l option displays multipath topology gathered from information in sysfs and the
device mapper. T he -ll option displays the information the -l displays in addition to all other available
components of the system.
When displaying the multipath configuration, there are three verbosity levels you can specify with the -v
option of the m ultipath command. Specifying -v0 yields no output. Specifying -v1 outputs the created
or updated multipath names only, which you can then feed to other tools such as kpartx. Specifying v2 prints all detected paths, multipaths, and device maps.
T he following example shows the output of a m ultipath -l command.
# multipath -l
mpath1 (3600d0230003228bc000339414edb8101)
[size=10 GB][features="0"][hwhandler="0"]
\_ round-robin 0 [prio=1][active]
\_ 2:0:0:6 sdb 8:16 [active][ready]
\_ round-robin 0 [prio=1][enabled]
\_ 3:0:0:6 sdc 8:64 [active][ready]
5.3. Multipath Command Options
T able 5.1, “Useful m ultipath Command Options” describes some options of the m ultipath
command that you may find useful.
T able 5.1. Useful m ultipath Command Options
Option
Description
-l
Display the current multipath configuration gathered from sysfs and
the device mapper.
-ll
Display the current multipath configuration gathered from sysfs, the
device mapper, and all other available components on the system.
-f device
Remove the named multipath device.
-F
Remove all multipath devices.
5.4. Determining Device Mapper Entries with the dmsetup
Command
You can use the dm setup command to find out which device mapper entries match the multipathed
devices.
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Red Hat Enterprise Linux 4 D M Multipath
T he following command displays all the device mapper devices and their major and minor numbers. T he
minor numbers determine the name of the dm device. For example, a minor number of 3 corresponds to
the multipathed device /dev/dm -3.
# dmsetup ls
mpath2 (253, 4)
mpath4p1
(253,
mpath5p1
(253,
mpath1 (253, 3)
mpath6p1
(253,
mpath7p1
(253,
mpath0 (253, 2)
mpath7 (253, 9)
mpath6 (253, 8)
VolGroup00-LogVol01
mpath5 (253, 7)
VolGroup00-LogVol00
mpath4 (253, 6)
mpath1p1
(253,
mpath3 (253, 5)
12)
11)
14)
13)
(253, 1)
(253, 0)
10)
5.5. Troubleshooting with the multipathd Interactive Console
T he m ultipathd -k command is an interactive interface to the m ultipathd daemon. Entering this
command brings up an interactive multipath console. After entering this command, you can enter help to
get a list of available commands, you can enter a interactive command, or you can enter CT RL-D to quit.
T he m ultipathd interactive console can be used to troubleshoot problems you may be having with
your system. For example, the following command sequence displays the multipath configuration,
including the defaults, before exiting the console.
# multipathd -k
> > show config
> > CTRL-D
T he following command sequence ensures that multipath has picked up any changes to the
m ultipath.conf,
# multipathd -k
> > reconfigure
> > CTRL-D
Use the following command sequence to ensure that the path checker is working properly.
# multipathd -k
> > show paths
> > CTRL-D
5.6. Resizing an Online Multipathed Device (RHEL 4.8 and later)
In systems running RHEL 4.8 and later, is is possible to resize a multipath device while it is online. T his
allows you to resize the device when it is open, as when a file system is currently mounted.
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Chapter 5. D M-Multipath Administration and Troubleshooting
Use the following procedure to resize an online multipath device.
1. Resize your physical device.
2. Resize your paths. For SCSI devices, writing a 1 to the rescan file for the device causes the SCSI
driver to rescan. You can use the following command:
# echo 1 > /sys/block/device_name/device/rescan
3. Resize your multipath device by running the m ultipath command:
#
multipath
Your hardware setup may require that you temporarily take the actual storage offline in order to resize
your physical device. If you take your storage offline and your multipath device is not set to queue when
all paths are down, any I/O activity while your storage is offline will fail. You can work around this by
executing the following command before taking your storage offline:
#
dmsetup suspend --noflush device_name
After you resize your storage and take it back online, you must run the following command before
resizing your paths:
#
dmsetup resume device_name
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Red Hat Enterprise Linux 4 D M Multipath
Revision History
Revision 1.0-11.4 00
Rebuild with publican 4.0.0
2013-10-31
Rüdiger Landmann
Revision 1.0-11
Rebuild for Publican 3.0
2012-07-18
Anthony T owns
Revision 4 .9-1
Resolves: #633518
Fixes typo.
Wed Feb 16 2011
Steven Levine
Revision 1.0-0
Wed Apr 01 2009
Index
A
active/active configuration
- definition, Overview of DM-Multipath
- illustration, Overview of DM-Multipath
active/passive configuration
- definition, Overview of DM-Multipath
- illustration, Overview of DM-Multipath
alias parameter , Multipaths Device Configuration Attributes
- configuration file, Multipath Device Identifiers
B
bindings_file parameter, Configuration File Defaults
blacklist
-
configuration file, Configuration File Blacklist
default devices, Blacklisting By Device Name
device name, Blacklisting By Device Name
in configuration file, Setting Up DM-Multipath
WWID, Blacklisting By WWID
bl_product parameter, Configuration File Devices
C
chkconfig command, Setting Up DM-Multipath
configuration file
- alias parameter, Multipaths Device Configuration Attributes
- bindings_file parameter, Configuration File Defaults
34
Revision History
- blacklist, Setting Up DM-Multipath, Configuration File Blacklist
- bl_product parameter, Configuration File Devices
- devnode_blacklist, Configuration File Blacklist
- failback parameter, Configuration File Defaults, Multipaths Device Configuration Attributes,
Configuration File Devices
- features parameter, Configuration File Defaults, Configuration File Devices
- flush_on_last_del parameter, Configuration File Defaults
- getuid_callout parameter, Configuration File Defaults, Configuration File Devices
- gid parameter, Configuration File Defaults
- hardware_handler parameter, Configuration File Devices
- max_fds parameter, Configuration File Devices
- mode parameter, Configuration File Defaults
- no_path_retry parameter, Configuration File Defaults, Multipaths Device Configuration
Attributes, Configuration File Devices
- overview, Configuration File Overview
- path_checker parameter, Configuration File Defaults, Configuration File Devices
- path_grouping_policy parameter, Configuration File Defaults, Multipaths Device
Configuration Attributes, Configuration File Devices
- path_selector parameter, Multipaths Device Configuration Attributes, Configuration File
Devices
- polling-interval parameter, Configuration File Defaults
- prio_callout parameter, Configuration File Defaults, Configuration File Devices
- product parameter, Configuration File Devices
- rr_min_io parameter, Configuration File Defaults, Multipaths Device Configuration
Attributes
- rr_weight parameter, Configuration File Defaults, Multipaths Device Configuration
Attributes, Configuration File Devices
- selector parameter, Configuration File Defaults
- udev_dir parameter, Configuration File Defaults
- uid parameter, Configuration File Defaults
- user_friendly_names parameter, Configuration File Defaults
- vendor parameter, Configuration File Devices
- wwid parameter, Multipaths Device Configuration Attributes
configuring
- DM-Multipath, Setting Up DM-Multipath
D
defaults section
- multipath.conf file, Configuration File Defaults
dev/mapper directory, Multipath Device Identifiers
dev/mpath directory, Multipath Device Identifiers
device name, Multipath Device Identifiers
device-mapper-multipath package, Setting Up DM-Multipath
devices
- adding, Adding Devices to the Multipathing Database , Configuration File Devices
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Red Hat Enterprise Linux 4 D M Multipath
devices section
- multipath.conf file, Configuration File Devices
devnode_blacklist
- configuration file, Configuration File Blacklist
DM-Multipath
- and LVM, Multipath Devices in Logical Volumes
- components, DM-Multipath Components
- configuration file, T he DM-Multipath Configuration File
- configuring, Setting Up DM-Multipath
- definition, Device Mapper Multipathing
- device name, Multipath Device Identifiers
- devices, Multipath Devices
- failover, Overview of DM-Multipath
- overview, Overview of DM-Multipath
- redundancy, Overview of DM-Multipath
- setup, Setting Up DM-Multipath
- setup, overview, DM-Multipath Setup Overview
dm-multipath kernel module , DM-Multipath Components
dm-n devices, Multipath Device Identifiers
dmsetup command, determining device mapper entries, Determining Device Mapper
Entries with the dmsetup Command
E
etc/multipath.conf package, Setting Up DM-Multipath
F
failback parameter, Configuration File Defaults, Multipaths Device Configuration
Attributes, Configuration File Devices
failover, Overview of DM-Multipath
features parameter, Configuration File Defaults, Configuration File Devices
feedback, Feedback
flush_on_last_del parameter, Configuration File Defaults
G
getuid_callout parameter, Configuration File Defaults, Configuration File Devices
gid parameter, Configuration File Defaults
H
hardware_handler parameter, Configuration File Devices
K
36
Revision History
kpartx command , DM-Multipath Components
L
local disks, ignoring, Ignoring Local Disks when Generating Multipath Devices
LVM physical volumes
- multipath devices, Multipath Devices in Logical Volumes
lvm.conf file , Multipath Devices in Logical Volumes
M
max_fds parameter, Configuration File Devices
mode parameter, Configuration File Defaults
modprobe command, Setting Up DM-Multipath
multipath command , DM-Multipath Components, Setting Up DM-Multipath
- options, Multipath Command Options
- output, Multipath Command Output
- queries, Multipath Queries with multipath Command
multipath devices, Multipath Devices
- logical volumes, Multipath Devices in Logical Volumes
- LVM physical volumes, Multipath Devices in Logical Volumes
multipath.conf file, Storage Array Support, T he DM-Multipath Configuration File
- defaults section, Configuration File Defaults
- devices section, Configuration File Devices
- multipaths section, Multipaths Device Configuration Attributes
multipath.conf.annotated file, T he DM-Multipath Configuration File
multipath.conf.defaults file, Storage Array Support, T he DM-Multipath Configuration File
multipathd
- command, T roubleshooting with the multipathd Interactive Console
- interactive console, T roubleshooting with the multipathd Interactive Console
multipathd daemon , DM-Multipath Components
multipathd start command, Setting Up DM-Multipath
multipaths section
- multipath.conf file, Multipaths Device Configuration Attributes
N
no_path_retry parameter, Configuration File Defaults, Multipaths Device Configuration
Attributes, Configuration File Devices
37
Red Hat Enterprise Linux 4 D M Multipath
P
path_checker parameter, Configuration File Defaults, Configuration File Devices
path_grouping_policy parameter, Configuration File Defaults, Multipaths Device
Configuration Attributes, Configuration File Devices
path_selector parameter, Multipaths Device Configuration Attributes, Configuration File
Devices
polling_interval parameter, Configuration File Defaults
prio_callout parameter, Configuration File Defaults, Configuration File Devices
product parameter, Configuration File Devices
R
rr_min_io parameter, Configuration File Defaults, Multipaths Device Configuration
Attributes
rr_weight parameter, Configuration File Defaults, Multipaths Device Configuration
Attributes, Configuration File Devices
S
selector parameter, Configuration File Defaults
setup
- DM-Multipath, Setting Up DM-Multipath
storage array support, Storage Array Support
storage arrays
- adding, Adding Devices to the Multipathing Database , Configuration File Devices
U
udev_dir parameter, Configuration File Defaults
uid parameter, Configuration File Defaults
user_friendly_names parameter , Multipath Device Identifiers, Configuration File
Defaults
V
vendor parameter, Configuration File Devices
W
World Wide Identifier (WWID), Multipath Device Identifiers
wwid parameter, Multipaths Device Configuration Attributes
38
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