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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. These 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.
This chapter provides a summary of the features of DM-Multipath that
are new for the initial release of Red Hat Enterprise Linux 6. Following
that, this chapter provides a high-level overview of DM Multipath and
its components, as well as an overview of DM-Multipath setup.
1.1. New and Changed Features
This section lists new and changed features of DM-Multipath that are
included with the initial release of Red Hat Enterprise Linux 6.
For the Red Hat Enterprise Linux 6 release, the initial
DM-Multipath setup procedure for a basic failover configuration has
changed. You can now create the DM-Multipath configuration file and
enable DM-Multipath with the mpathconf configuration utility, which can also load the device-mapper-multipath module, start the multipathd daemon, and set chkconfig to start the daemon automatically on reboot.
The Red Hat Enterprise Linux 6 release provides a new mode for setting up multipath devices, which you set with the find_multipaths
configuration file parameter. In previous releases of Red Hat
Enterprise Linux, multipath always tried to create a multipath device
for every path that was not explicitly blacklisted. In Red Hat
Enterprise Linux 6, however, if the find_multipath configuration parameter is set to yes, then multipath will create a device only if one of three conditions are met:
There are at least two non-blacklisted paths with the same WWID.
The user manually forces the device creation, by specifying a device with the multipath command.
A path has the same WWID as a multipath device that was
previously created (even if that multipath device does not currently
exist). For instructions on the procedure to follow if you have
previously created multipath devices when the
find_multipaths parameter was not set, see
Section 4.2, “Configuration File Blacklist”.
This feature should allow most users to have multipath
automatically choose the correct paths to make into multipath devices,
without having to edit the blacklist.
The Red Hat Enterprise Linux 6 release provides two new path
selector algorithms which determine which path to use for the next I/O
operation:
queue-length and
service-time. The
queue-length algorithm looks at the amount of outstanding I/O to the paths to determine which path to use next. The
service-time
algorithm looks at the amount of outstanding I/O and the relative
throughput of the paths to determine which path to use next. For more
information on the path selector parameters in the configuration file,
see
Chapter 4, The DM-Multipath Configuration File.
In the Red Hat Enterprise Linux 6 release, priority functions are
no longer callout programs. Instead they are dynamic shared objects like
the path checker functions. The
prio_callout parameter has been replaced by the
prio parameter. For descriptions of the supported
prio functions, see
Chapter 4, The DM-Multipath Configuration File.
In the Red Hat Enterprise Linux 6 release, the location of the multipath bindings file is /etc/multipath/bindings.
The Red Hat Enterprise Linux 6 release provides three new
defaults parameters in the
multipath.conf file:
checker_timeout,
fast_io_fail_tmo, and
dev_loss_tmo. For information on these parameters, see
Chapter 4, The DM-Multipath Configuration File.
When the user_friendly_names option in the multipath configuration file is set to yes, the name of a multipath device is of the form mpathn. For the Red Hat Enterprise Linux 6 release, n is an alphabetic character, so that the name of a multipath device might be mpatha or mpathb. In previous releases, n was an integer.
1.2. 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 round-robin fashion. In some configurations,
DM-Multipath can detect loading on the I/O paths and dynamically
re-balance the load.
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. There are many points of possible failure in this
configuration:
With DM-Multipath configured, a failure at any of these points will cause DM-Multipath to switch to the alternate I/O path.
hba1 to controller1
hba1 to controller2
hba2 to controller1
hba2 to controller2
In this configuration, I/O can be spread among those four paths.
1.3. Storage Array Support
By default, DM-Multipath includes support for the most common storage
arrays that support DM-Multipath. The supported devices can be found in
the
multipath.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,
multipath.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. These require separate hardware handler kernel modules.
1.4. DM-Multipath Components
Table 1.1. DM-Multipath Components
|
Component
|
Description
|
|---|
dm_multipath kernel module
|
Reroutes I/O and supports failover for paths and path groups.
|
mpathconf utility
|
Configures and enables device mapper multipathing.
|
multipath 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 initramfs file system.
|
multipathd daemon
|
Monitors paths; as paths fail and come back, it may initiate path
group switches. Provides for interactive changes to multipath devices.
This must be restarted for any changes to the /etc/multipath.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 DM-MP.
The kpartx is provided in its own package, but the device-mapper-multipath package depends on it.
|
1.5. 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.
The basic procedure for configuring your system with DM-Multipath is as follows:
Install the device-mapper-multipath rpm.
Create the configuration file and enable multipathing with the mpathconf command. You can also start the multipath daemon with this command if you do not need to edit the configuration file.
If necessary, edit the multipath.conf configuration file to modify default values and save the updated file.
Start the multipath daemon.
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_names option in the multipath configuration file, which sets the alias to a node-unique name of the form mpathn.
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_names configuration option is set to yes, the name of the multipath device is set to mpathn.
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/mapper/mpathn, /dev/mpath/mpathn, and /dev/dm-n.
The devices in /dev/mapper are
created early in the boot process. Use these devices to access the
multipathed devices, for example when creating logical volumes.
The devices in /dev/mpath are provided as a convenience so that all multipathed devices can be seen in one directory. These 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.
You can also set the name of a multipath device to a name of your choosing by using the
alias option in the
multipaths section of the multipath configuration file. For information on the
multipaths section of the multipath configuration file, see
Section 4.4, “Multipaths Device Configuration Attributes”.
2.2. Consistent Multipath Device Names in a Cluster
When the user_friendly_names 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.
Similarly, if you set the alias option for a device in the multipaths section of the multipath.conf
configuration file, the name is not automatically consistent across all
nodes in the cluster. This 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 it
is recommended that you not set the user_friendly_names option to yes and that you not configure aliases for the devices. By default, if you do not set user_friendly_names to yes or configure an alias for a device, a device name will be the WWID for the device, which is always the same.
If you want the system-defined user-friendly names to be consistent
across all nodes in the cluster, however, you can follow this procedure:
Set up all of the multipath devices on one machine.
Disable all of your multipath devices on your other machines.
Copy the /etc/multipath/bindings file from the first machine to all the other machines in the cluster.
If you add a new device, you will need to repeat this process.
Similarly, if you configure an alias for a device that you would like
to be consistent across the nodes in the cluster, you should ensure
that the /etc/multipath.conf file is the same for each node in the cluster by following the same procedure:
Configure the aliases for the multipath devices in the in the multipath.conf file on one machine.
Disable all of your multipath devices on your other machines.
Copy the /etc/multipath.conf file from the first machine to all the other machines in the cluster.
When you add a new device you will need to repeat this process.
2.3. Multipath Device Attributes
In addition to the
user_friendly_names 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
multipaths section of the multipath configuration file. For information on the
multipaths 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/mapper/mpatha is the name of a multipath device, the following command will mark /dev/mapper/mpatha as a physical volume.
pvcreate /dev/mapper/mpatha
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.
If you attempt to create an LVM physical volume on a whole device on which you have configured partitions, the pvcreate
command will fail. Note that the Anaconda and Kickstart installation
programs create empty partition tables if you do not specify otherwise
for every block device. If you wish to use the whole device rather than a
partition, you must remove the existing partitions from the device. You
can remove existing partitions with the kpartx -d and the fdisk commands. If your system has block devices that are greater that 2Tb, you can use the parted command to remove partitions.
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 to exclude the
disks that underlie the multipath devices. This 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.
To filter all SCSI devices in the LVM configuration file (lvm.conf), include the following filter in the devices section of the file.
filter = [ "r/disk/", "r/sd.*/", "a/.*/" ]
Chapter 3. Setting Up DM-Multipath
This chapter provides step-by-step example procedures for configuring DM-Multipath. It includes the following procedures:
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-mapper-multipath package.
You set up multipath with the mpathconf utility, which creates the multipath configuration file /etc/multipath.conf.
If the /etc/multipath.conf file already exists, the mpathconf utlity will edit it.
If the /etc/multipath.conf file does not exist, the mpathconf utility will use the /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf file as the starting file.
If the /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf file does not exist the mpathconf utility will create the /etc/multipath.conf file from scratch.
If you do not need to edit the /etc/multipath.conf
file, you can set up DM-Multipath for a basic failover configuration by
running the following command. This command enables the multipath
configuration file and starts the multipathd daemon.
# mpathconf --enable --with_multipathd y
If you need to edit the /etc/multipath.conf file before starting the multipathd daemon. use the following procedure to set up DM-Multipath for a basic failover configuration.
Run the mpathconf command with the --enable option specified:
# mpathconf --enable
For information on additional options to the mpathconf command you may require, see the mpathconf man page or run the mpathconf command with the --help option specified.
# mpathconf --help
usage: /sbin/mpathconf <command>
Commands:
Enable: --enable
Disable: --disable
Set user_friendly_names (Default n): --user_friendly_names <y|n>
Set find_multipaths (Default n): --find_multipaths <y|n>
Load the dm-multipath modules on enable (Default y): --with_module <y|n>
start/stop/reload multipathd (Default n): --with_multipathd <y|n>
chkconfig on/off multipathd (Default y): --with_chkconfig <y|n>
Edit the /etc/multipath.conf file if
necessary. The default settings for DM-Multipath are compiled in to the
system and do not need to be explicitly set in the /etc/multipath.conf file.
The default value of
path_grouping_policy is set to
failover, so in this example you do not need to edit the
/etc/multipath.conf file. For information on changing the values in the configuration file to something other than the defaults, see
Chapter 4, The DM-Multipath Configuration File.
The initial defaults section of the configuration file configures
your system so that the names of the multipath devices are of the form mpathn; without this setting, the names of the multipath devices would be aliased to the WWID of the device.
Save the configuration file and exit the editor, if necessary.
Execute the following command:
# service multipathd start
Since the value of
user_friendly_name is set to
yes in the configuration file, the multipath devices will be created as
/dev/mapper/mpathn. For information on setting the name of the device to an alias of your choosing, see
Chapter 4, The DM-Multipath Configuration File.
If you do not want to use user friendly names, you can run the following command:
# mpathconf --enable --user_friendly_names n
If you find that you need to edit the multipath configuration file
after you have started the multipath daemon, you must execute the service multipath reload command for the changes to take effect.
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. If you set the
find_multipaths configuration parameter to
yes, you should not have to blacklist these devices. For information on the
find_multipaths configuration parameter, see
Section 4.3, “Configuration File Defaults”.
If you do not set the find_multipaths configuration parameter to yes,
can use the following procedure to modify the multipath configuration
file to ignore the local disks when configuring multipath.
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 multipath -v2 shows the local disk, /dev/sda, in the multipath map.
[root@rh4cluster1 ~]# multipath -v2
create: SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1 undef WINSYS,SF2372
size=33 GB features="0" hwhandler="0" wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 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 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:0 sdb 8:16 undef ready running
`- 3:0:0:0 sdf 8:80 undef ready running
create: 3600a0b80001327510000009a436215ec undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:1 sdc 8:32 undef ready running
`- 3:0:0:1 sdg 8:96 undef ready running
create: 3600a0b80001327d800000070436216b3 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:2 sdd 8:48 undef ready running
`- 3:0:0:2 sdg 8:112 undef ready running
create: 3600a0b80001327510000009b4362163e undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:3 sdd 8:64 undef ready running
`- 3:0:0:3 sdg 8:128 undef ready running
In order to prevent the device mapper from mapping /dev/sda in its multipath maps, edit the blacklist section of the /etc/multipath.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. To blacklist individual devices, you can blacklist using the WWID of that device.
Note that in the output to the multipath -v2 command, the WWID of the /dev/sda device is SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1. To blacklist this device, include the following in the /etc/multipath.conf file.
blacklist {
wwid SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
}
After you have updated the /etc/multipath.conf file, you must manually tell the multipathd daemon to reload the file. The following command reloads the updated /etc/multipath.conf file.
[root@rh4cluster1 ~]# service multipathd reload
Run the following command to remove the multipath device:
[root@rh4cluster1 ~]# multipath -f SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1
To check that the blacklisted device was not added back, you can run the multipath command, as in the following example. The multipath command defaults to a verbosity level of v2 if you do not specify specify a -v option.
[root@rh4cluster1 ~]# multipath
create: 3600a0b80001327d80000006d43621677 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:0 sdb 8:16 undef ready running
`- 3:0:0:0 sdf 8:80 undef ready running
create: 3600a0b80001327510000009a436215ec undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:1 sdc 8:32 undef ready running
`- 3:0:0:1 sdg 8:96 undef ready running
create: 3600a0b80001327d800000070436216b3 undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:2 sdd 8:48 undef ready running
`- 3:0:0:2 sdg 8:112 undef ready running
create: 3600a0b80001327510000009b4362163e undef WINSYS,SF2372
size=12G features='0' hwhandler='0' wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
|- 2:0:0:3 sdd 8:64 undef ready running
`- 3:0:0:3 sdg 8:128 undef ready running
3.3. Configuring Storage Devices
By default, DM-Multipath includes support for the most common storage
arrays that support DM-Multipath. The default configuration values,
including supported devices, can be found in the multipath.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/multipath.conf file and insert the appropriate device information.
For example, to add information about the HP Open-V series the entry looks like this, where %n is the device name:
devices {
device {
vendor "HP"
product "OPEN-V."
getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n"
}
}
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. The
default configuration values and the supported devices can be found in
the /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf.defaults file.
You can override the default configuration values for DM-Multipath by editing the /etc/multipath.conf
configuration file. If necessary, you can also add a storage array that
is not supported by default to the configuration file. This chapter
provides information on parsing and modifying the multipath.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 multipath.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.
The configuration file allows regular expression description syntax.
An annotated version of the configuration file can be found in /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf.annotated.
4.1. Configuration File Overview
The multipath configuration file is divided into the following sections:
- blacklist
Listing of specific devices that will not be considered for multipath.
- blacklist_exceptions
Listing of multipath candidates that would otherwise be blacklisted according to the parameters of the blacklist section.
- defaults
General default settings for DM-Multipath.
- multipaths
Settings for the characteristics of individual multipath devices. These values overwrite what is specified in the defaults and devices sections of the configuration file.
- devices
Settings for the individual storage controllers. These 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
The 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.
In older releases of Red Hat Enterprise Linux, multipath always tried
to create a multipath device for every path that was not explicitly
blacklisted. In Red Hat Enterprise Linux 6, however, if the find_multipath configuration parameter is set to yes, then multipath will create a device only if one of three conditions are met:
There are at least two non-blacklisted paths with the same WWID.
The user manually forces the creation of the device by specifying a device with the multipath command.
A path has the same WWID as a multipath device that was previously
created (even if that multipath device does not currently exist).
Whenever a multipath device is created, multipath remembers the WWID of
the device so that it will automatically create the device again as soon
as it sees a path with that WWID. This allows you to have multipath
automatically choose the correct paths to make into multipath devices,
without have to edit the multipath blacklist.
If you have previously created a multipath device without using the find_multipaths parameter and then you later set the parameter to yes, you may need to remove the WWIDs of any device you do not want created as a multipath device from the /etc/multipath/wwids file. The following shows a sample /etc/multipath/wwids file. The WWIDs are enclose by slashes (/):
# Multipath wwids, Version : 1.0
# NOTE: This file is automatically maintained by multipath and multipathd.
# You should not need to edit this file in normal circumstances.
#
# Valid WWIDs:
/3600d0230000000000e13955cc3757802/
/3600d0230000000000e13955cc3757801/
/3600d0230000000000e13955cc3757800/
/3600d02300069c9ce09d41c31f29d4c00/
/SWINSYS SF2372 0E13955CC3757802/
/3600d0230000000000e13955cc3757803/
With the find_multipaths parameter set to yes,
you need to blacklist only the devices with multiple paths that you do
not want to be multipathed. Because of this, it will generally not be
necessary to blacklist devices.
If you do need to blacklist devices, you can do so according to the following criteria:
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.
The 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 blacklist section of the configuration file.
The following example shows the lines in the configuration file that
would blacklist all SCSI devices, since it blacklists are sd* devices.
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 a specific type. This is not
recommended, however, since 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. To enable
multipathing on any of these devices, you would need to specify them in
the
blacklist_exceptions section of the configuration file, as described in
Section 4.2.4, “Blacklist Exceptions”.
blacklist {
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^hd[a-z]"
}
4.2.3. Blacklisting By Device Type
You can specify specific device types in the blacklist section of the configuration file with a device section. The following example blacklists all IBM DS4200 device and all HP devices.
blacklist {
device {
vendor "IBM"
product "3S42" #DS4200 Product 10
}
device {
vendor "HP"
product "*"
}
}
4.2.4. Blacklist Exceptions
You can use the blacklist_exceptions section of the configuration file to enable multipathing on devices that have been blacklisted by default.
For example, if you have a large number of devices and want to
multipath only one of them (with the WWID of
3600d0230000000000e13955cc3757803), instead of individually blacklisting
each of the devices except the one you want, you could instead
blacklist all of them, and then allow only the one you want by adding
the following lines to the /etc/multipath.conf file.
blacklist {
wwid "*"
}
blacklist_exceptions {
wwid "3600d0230000000000e13955cc3757803"
}
When specifying devices in the blacklist_exceptions
section of the configuration file, you must specify the exceptions in
the same way they were specified in the blacklist. For example, a WWID
exception will not apply to devices specified by a devnode blacklist entry, even if the blacklisted device is associated with that WWID. Similarly, devnode exceptions apply only to devnode entries, and device exceptions apply only to device entries.
4.3. Configuration File Defaults
The /etc/multipath.conf configuration file includes a defaults section that sets the user_friendly_names parameter to yes, as follows.
defaults {
user_friendly_names yes
}
This overwrites the default value of the user_friendly_names parameter.
The configuration file includes a template of configuration defaults. This section is commented out, as follows.
#defaults {
# udev_dir /dev
# polling_interval 5
# selector "round-robin 0"
# path_grouping_policy failover
# getuid_callout "/lib/dev/scsi_id --whitelisted --device=/dev/%n"
# prio const
# path_checker directio
# rr_min_io 1000
# rr_weight uniform
# failback manual
# no_path_retry fail
# user_friendly_names no
#}
To 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 multibus 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.
defaults {
user_friendly_names yes
path_grouping_policy multibus
}
Table 4.1, “Multipath Configuration Defaults” describes the attributes that are set in the
defaults section of the
multipath.conf configuration file. These values are used by DM-Multipath unless they are overwritten by the attributes specified in the
devices and
multipaths sections of the
multipath.conf file.
Table 4.1. Multipath Configuration Defaults
|
Attribute
|
Description
|
|---|
polling_interval
|
Specifies the interval between two path checks in seconds. For
properly functioning paths, the interval between checks will gradually
increase to (4 * polling_interval). The default value is 5.
|
udev_dir
|
The directory where udev device nodes are created. The default value is /dev.
|
multipath_dir
|
The directory where the dynamic shared objects are stored. The default value is system dependent, commonly /lib/multipath.
|
find_multipaths
|
Defines the mode for setting up multipath devices. If this parameter is set to yes,
then multipath will not try to create a device for every
non-blacklisted path. Instead multipath will create a device only if one
of three conditions are met: | | - There are at least two non-blacklisted paths with the same WWID. | - The user manually forces the creation of the device by specifying a device with the multipath command. | - A path has the same WWID as a multipath device that was previously created. Whenever a multipath device is created with find_multipaths
set, multipath remembers the WWID of the device so that it will
automatically create the device again as soon as it sees a path with
that WWID. This allows you to have multipath automatically choose the
correct paths to make into multipath devices, without having to edit the
multipath blacklist. For instructions on the procedure to follow if you
have previously created multipath devices when the find_multipaths parameter was not set, see Section 4.2, “Configuration File Blacklist”. | The default value is no. |
|
verbosity
|
The default verbosity. Higher values increase the verbosity
level. Valid levels are between 0 and 6. The default value is 2.
|
path_selector
|
| Specifies the default algorithm to use in determining what path to use for the next I/O operation. Possible values include: | round-robin 0: Loop through every path in the path group, sending the same amount of I/O to each. | queue-length 0: Send the next bunch of I/O down the path with the least number of outstanding I/O requests. | service-time 0:
Send the next bunch of I/O down the path with the shortest estimated
service time, which is determined by dividing the total size of the
outstanding I/O to each path by its relative throughput. | The 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. | multibus: 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. Priorities are determined by
callout programs specified as global, per-controller, or per-multipath
options. | group_by_node_name: 1 priority group per target node name. Target node names are fetched in /sys/class/fc_transport/target*/node_name. | The default value is multibus. |
|
getuid_callout
|
| Specifies the default program and arguments to call out to obtain a unique path identifier. An absolute path is required. | The default value is /lib/udev/scsi_id --whitelisted --device=/dev/%n. |
|
prio
|
Specifies the default function to call to obtain a path priority value.
For example, the ALUA bits in SPC-3 provide an exploitable prio value. Possible values include: | const: Set a priority of 1 to all paths. | emc: Generate the path priority for EMC arrays. | alua: Generate the path priority based on the SCSI-3 ALUA settings. | tpg_pref: Generate the path priority based on the SCSI-3 ALUA settings, using the preferred port bit. | ontap: Generate the path priority for NetApp arrays. | rdac: Generate the path priority for LSI/Engenio RDAC controller. | hp_sw: Generate the path priority for Compaq/HP controller in active/standby mode. | hds: Generate the path priority for Hitachi HDS Modular storage arrays. | The default value is const. |
|
features
|
The default extra features of multipath devices. The only existing feature is queue_if_no_path, which is the same as setting no_path_retry to queue. For information on issues that may arise when using this feature, see Section 5.4, “Issues with queue_if_no_path feature”.
|
path_checker
|
| Specifies the default method used to determine the state of the paths. Possible values include: | readsector0: Read the first sector of the device. | tur: Issue a TEST UNIT READY to the device. | emc_clariion: Query the EMC Clariion specific EVPD page 0xC0 to determine the path. | hp_sw: Check the path state for HP storage arrays with Active/Standby firmware. | rdac: Check the path stat for LSI/Engenio RDAC storage controller. | directio: Read the first sector with direct I/O. | The default value is readsector0. |
|
failback
|
| Manages path group failback. | A value of immediate specifies immediate failback to the highest priority path group that contains active paths. | A value of manual specifies that there should not be immediate failback but that failback can happen only with operator intervention. | A value of followover
specifies that automatic failback should be performed when the first
path of a path group becomes active. This keeps a node from
automatically failing back when another node requested the failover. | | A numeric value greater than zero specifies deferred failback, expressed in seconds. | The default value is manual. |
|
rr_min_io
|
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group. The default value
is 1000.
|
rr_weight
|
If set to priorities, then instead of sending rr_min_io requests to a path before calling path_selector to choose the next path, the number of requests to send is determined by rr_min_io times the path's priority, as determined by the prio function. If set to uniform, all path weights are equal. The 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. | | The default value is 0. |
|
user_friendly_names
|
If set to yes, specifies that the system should use the /etc/multipath/bindings file to assign a persistent and unique alias to the multipath, in the form of mpathn. 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 overriden by
any device-specific aliases you specify in the multipaths section of the configuration file. The default value is no.
|
queue_without_daemon
|
If set to no, the multipathd daemon will disable queueing for all devices when it is shut down. The default value is yes.
|
flush_on_last_del
|
If set to yes, the multipathd daemon will disable queueing when the last path to a device has been deleted. The default value is no.
|
max_fds
|
Sets the maximum number of open file descriptors that can be opened by multipath and the multipathd daemon. This is equivalent to the ulimit -n command. A value of max will set this to the system limit from /proc/sys/fs/nr_open.
If this is not set, the maximum number of open file descriptors is
taken from the calling process; it is usually 1024. To be safe, this
should be set to the maximum number of paths plus 32, if that number is
greater than 1024.
|
checker_timer
|
The timeout to use for path checkers that issue scsi commands
with an explicit timeout, in seconds. The default value is taken from sys/block/sdx/device/timeout.
|
fast_io_fail_tmo
|
The number of seconds the scsi layer will wait after a problem
has been detected on an FC remote port before failing I/O to devices on
that remote port. This value should be smaller than the value of dev_loss_tmo. Setting this to off will disable the timeout. The default value is determined by the OS.
|
dev_loss_tmo
|
The number of seconds the scsi layer will wait after a problem
has been detected on an FC remote port before removing it from the
system. The default value is determined by the OS.
|
mode
|
The mode to use for the multipath device nodes, in octal. The default value is determined by the process.
|
uid
|
The user ID to use for the multipath device nodes. You may use
either the numeric or symbolic user ID. The default value is determined
by the process.
|
gid
|
The group ID to use for the multipath device nodes. You may use
either the numeric or symbolic group ID. The default value is determined
by the process.
|
4.4. Multipaths Device Configuration Attributes
Table 4.2, “Multipath Attributes” shows the attributes that you can set in the
multipaths section of the
multipath.conf
configuration file for each specific multipath device. These attributes
apply only to the one specified multipath. These defaults are used by
DM-Multipath and override attributes set in the
defaults and
devices sections of the
multipath.conf file.
Table 4.2. Multipath Attributes
|
Attribute
|
Description
|
|---|
wwid
|
Specifies the WWID of the multipath device to which the multipath attributes apply. This parameter is mandatory for this section of the multipath.conf file.
|
alias
|
Specifies the symbolic name for the multipath device to which the multipath attributes apply. If you are using user_friendly_names, do not set this value to mpathn; this may conflict with an automatically assigned user friendly name and give you incorrect device node names.
|
path_grouping_policy
|
| Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include: | failover = 1 path per priority group | multibus = 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_name = 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. Possible values include: | round-robin 0: Loop through every path in the path group, sending the same amount of I/O to each. | queue-length 0: Send the next bunch of I/O down the path with the least number of outstanding I/O requests. | service-time 0:
Send the next bunch of I/O down the path with the shortest estimated
service time, which is determined by dividing the total size of the
outstanding I/O to each path by its relative throughput. | The default value is round-robin 0. |
|
failback
|
| Manages path group failback. | A value of immediate specifies immediate failback to the highest priority path group that contains active paths. | A value of manual specifies that there should not be immediate failback but that failback can happen only with operator intervention. | A value of followover
specifies that automatic failback should be performed when the first
path of a path group becomes active. This keeps a node from
automatically failing back when another node requested the failover. | | A numeric value greater than zero specifies deferred failback, expressed in seconds. | The default value is manual. |
|
prio
|
Specifies the default function to call to obtain a path priority value.
For example, the ALUA bits in SPC-3 provide an exploitable prio value. Possible values include: | const: Set a priority of 1 to all paths. | emc: Generate the path priority for EMC arrays. | alua: Generate the path priority based on the SCSI-3 ALUA settings. | tpg_pref: Generate the path priority based on the SCSI-3 ALUA settings, using the preferred port bit. | ontap: Generate the path priority for NetApp arrays. | rdac: Generate the path priority for LSI/Engenio RDAC controller. | hp_sw: Generate the path priority for Compaq/HP controller in active/standby mode. | hds: Generate the path priority for Hitachi HDS Modular storage arrays. |
|
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. |
|
rr_min_io
|
Specifies the number of I/O requests to route to a path before
switching to the next path in the current path group. The default value
is 1000.
|
rr_weight
|
If set to priorities, then instead of sending rr_min_io requests to a path before calling path_selector to choose the next path, the number of requests to send is determined by rr_min_io times the path's priority, as determined by the prio function. If set to uniform, all path weights are equal.
|
flush_on_last_del
|
If set to yes, then multipath will disable queueing when the last path to a device has been deleted. The default value is no.
|
mode
|
The mode to use for the multipath device nodes, in octal.
|
uid
|
The user ID to use for the multipath device nodes. You may use
the either the symbolic or numeric user ID. The default value is
determined by the process.
|
gid
|
The group ID to use for the multipath device nodes. You may use
either the symbolic or the numeric group ID. The default value is
determined by the process.
|
The following example shows multipath attributes specified in the
configuration file for two specific multipath devices. The first device
has a WWID of 3600508b4000156d70001200000b0000 and a symbolic name of yellow.
The second multipath device in the example has a WWID of 1DEC_____321816758474 and a symbolic name of red. In this example, the rr_weight attributes is set to priorities.
multipaths {
multipath {
wwid 3600508b4000156d70001200000b0000
alias yellow
path_grouping_policy multibus
path_checker readsector0
path_selector "round-robin 0"
failback manual
rr_weight priorities
no_path_retry 5
}
multipath {
wwid 1DEC_____321816758474
alias red
rr_weight priorities
}
}
4.5. Configuration File Devices
Table 4.3, “Device Attributes” shows the attributes that you can set for each individual storage device in the
devices section of the
multipath.conf configuration file. These attributes are used by DM-Multipath unless they are overwritten by the attributes specified in the
multipaths section of the
multipath.conf file for paths that contain the device. These attributes override the attributes set in the
defaults section of the
multipath.conf file.
Many devices that support multipathing are included by default in a
multipath configuration. The values for the devices that are supported
by default are listed in the multipath.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 configuration file for the device that overwrites those
values. You can copy the device configuration defaults from the multipath.conf.defaults file for the device and override the values that you want to change.
To add a device to this section of the configuration file that is not
configured automatically by default, you 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/model 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
The 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
multibus. Other parameters you may need to set are
no_path_retry and
rr_min_io, as described in
Table 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). This almost always
means that you set the path_checker to tur; this works for all SCSI devices that support the Test 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. The current available hardware handler is emc. If this is not sufficient for your device, you may not be able to configure the device for multipath.
Table 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.
|
revision
|
Specifies the product revision identifier of the storage device.
|
product_blacklist
|
Specifies a regular expression used to blacklist devices by product.
|
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: | 1 emc: hardware handler for EMC storage arrays. | 1 alua: hardware handler for SCSI-3 ALUA arrays. | 1 hp_sw: hardware handler for Compaq/HP controllers. | 1 rdac: hardware handler for the LSI/Engenio RDAC controllers. |
|
path_grouping_policy
|
| Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include: | failover = 1 path per priority group | multibus = 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_name = 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.
|
path_selector
|
| Specifies the default algorithm to use in determining what path to use for the next I/O operation. Possible values include: | round-robin 0: Loop through every path in the path group, sending the same amount of I/O to each. | queue-length 0: Send the next bunch of I/O down the path with the least number of outstanding I/O requests. | service-time 0:
Send the next bunch of I/O down the path with the shortest estimated
service time, which is determined by dividing the total size of the
outstanding I/O to each path by its relative throughput. | The default value is round-robin 0. |
|
path_checker
|
| Specifies the default method used to determine the state of the paths. Possible values include: | readsector0: Read the first sector of the device. | tur: Issue a TEST UNIT READY to the device. | emc_clariion: Query the EMC Clariion specific EVPD page 0xC0 to determine the path. | hp_sw: Check the path state for HP storage arrays with Active/Standby firmware. | rdac: Check the path stat for LSI/Engenio RDAC storage controller. | directio: Read the first sector with direct I/O. | The default value is readsector0. |
|
features
|
The extra features of multipath devices. The only existing feature is queue_if_no_path, which is the same as setting no_path_retry to queue. For information on issues that may arise when using this feature, see Section 5.4, “Issues with queue_if_no_path feature”.
|
prio
|
Specifies the default function to call to obtain a path priority value.
For example, the ALUA bits in SPC-3 provide an exploitable prio value. Possible values include: | const: Set a priority of 1 to all paths. | emc: Generate the path priority for EMC arrays. | alua: Generate the path priority based on the SCSI-3 ALUA settings. | tpg_pref: Generate the path priority based on the SCSI-3 ALUA settings, using the preferred port bit. | ontap: Generate the path priority for NetApp arrays. | rdac: Generate the path priority for LSI/Engenio RDAC controller. | hp_sw: Generate the path priority for Compaq/HP controller in active/standby mode. | hds: Generate the path priority for Hitachi HDS Modular storage arrays. | The default value is const. |
|
failback
|
| Manages path group failback. | A value of immediate specifies immediate failback to the highest priority path group that contains active paths. | A value of manual specifies that there should not be immediate failback but that failback can happen only with operator intervention. | A value of followover
specifies that automatic failback should be performed when the first
path of a path group becomes active. This keeps a node from
automatically failing back when another node requested the failover. | | A numeric value greater than zero specifies deferred failback, expressed in seconds. | The default value is manual. |
|
rr_weight
|
If set to priorities, then instead of sending rr_min_io requests to a path before calling path_selector to choose the next path, the number of requests to send is determined by rr_min_io times the path's priority, as determined by the prio function. If set to uniform, all path weights are equal. The 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. | | The default value is 0. |
|
rr_min_io
|
The number of I/O requests to route to a path before switching to
the next path in the current path group. The default value is 1000.
|
fast_io_fail_tmo
|
The number of seconds the scsi layer will wait after a problem
has been detected on an FC remote port before failing I/O to devices on
that remote port. This value should be smaller than the value of dev_loss_tmo. Setting this to off will disable the timeout.
|
dev_loss_tmo
|
The number of seconds the scsi layer will wait after a problem
has been detected on an FC remote port before removing it from the
system.
|
flush_on_last_del
|
If set to yes, the multipathd daemon will disable queueing when the last path to a device has been deleted. The default value is no.
|
The 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
# }
#}
Chapter 5. DM-Multipath Administration and Troubleshooting
This chapter will provide information on administering DM-Multipath on
a running system. It includes sections on the following topics:
Resizing an Online Multipath Device
The Multipath Daemon
Issues with Large Number of LUNs
Issues with queue_if_no_path feature
Multipath Command Output
Multipath Queries with multipath Command
Multipath Command Options
Multipath Queries with dmsetup Command
Troubleshooting with the multipathd Interactive Console
5.1. Resizing an Online Multipath Device
If you need to resize an online multipath device, use the following procedure.
Resize your physical device.
Use the following command to find the paths to the LUN:
# multipath -l
Resize your paths. For SCSI devices, writing a 1 to the rescan file for the device causes the SCSI driver to rescan, as in the following command:
# echo 1 > /sys/block/device_name/device/rescan
Resize your multipath device by running the multipathd resize command:
# multipathd -k'resize map mpatha'
Resize the filesystem (assuming no LVM or DOS partitions are used):
# resize2fs /dev/mapper/mpatha
5.2. The Multipath Daemon
If you find you have trouble implementing a multipath configuration,
you should ensure that the multipath daemon is running, as described in
Chapter 3, Setting Up DM-Multipath. The
multipathd daemon must be running in order to use multipathed devices.
5.3. Issues with Large Number of LUNs
When a large number of LUNs are added to a node, using multipathed
devices can significantly increase the time it takes for the udev
device manager to create device nodes for them. If you experience this
problem, you can correct it by deleting the following line in /etc/udev/rules.d/40-multipath.rules:
KERNEL!="dm-[0-9]*", ACTION=="add", PROGRAM=="/bin/bash -c '/sbin/lsmod | /bin/grep ^dm_multipath'", RUN+="/sbin/multipath -v0 %M:%m"
This line causes the udev device manager to run multipath every time a block device is added to the node. Even with this line removed, the multipathd daemon will still automatically create multipathed devices, and multipath
will still be called during the boot process for nodes with multipathed
root file systems. The only change is that multipathed devices will not
be automatically created when the multipathd daemon is not running, which should not be a problem for the vast majority of multipath users.
5.4. Issues with queue_if_no_path feature
If features "1 queue_if_no_path" is specified in the /etc/multipath.conf file, then any process that issues I/O will hang until one or more paths are restored. To avoid this, set the no_path_retry N parameter in the /etc/multipath.conf file (where N is the number of times the system should retry a path).
When you set the no_path_retry parameter, remove the features "1 queue_if_no_path" option from the /etc/multipath.conf file as well. If, however, you are using a multipathed device for which the features "1 queue_if_no_path" option is set as a compiled-in default, as it is for many SAN devices, you must explicitly add features "0" to override this default. You can do this by copying the existing devices section for your device from /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf.defaults into /etc/multipath.conf and editing it to suit your needs.
If you need to use the features "1 queue_if_no_path" option and you experience the issue noted here, use the dmsetup
command to edit the policy at runtime for a particular LUN (that is,
for which all the paths are unavailable). For example, if you want to
change the policy on the multipath device mpathc from "queue_if_no_path" to "fail_if_no_path", execute the following command.
dmsetup message mpathc 0 "fail_if_no_path"
Note that you must specify the mpathn alias rather than the path.
5.5. Multipath Command Output
When you create, modify, or list a multipath device, you get a
printout of the current device setup. The format is as follows.
For each multipath device:
action_if_any: alias (wwid_if_different_from_alias) dm_device_name_if_known vendor,product size=size features='features' hwhandler='hardware_handler' wp=write_permission_if_known
For each path group:
-+- policy='scheduling_policy' prio=prio_if_known status=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:
3600d0230000000000e13955cc3757800 dm-1 WINSYS,SF2372
size=269G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 6:0:0:0 sdb 8:16 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 7:0:0:0 sdf 8:80 active ready running
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. The path status is updated periodically by the multipathd daemon based on the polling interval defined in the /etc/multipath.conf file.
The dm status is similar to the path status, but from the kernel's point of view. The 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.
When a multipath device is being created or modified, the path group
status, the dm device name, the write permissions, and the dm status
are not known. Also, the features are not always correct.
5.6. Multipath Queries with multipath Command
You can use the -l and -ll options of the multipath command to display the current multipath configuration. The -l option displays multipath topology gathered from information in sysfs and the device mapper. The -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 multipath 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.
The following example shows the output of a multipath -l command.
# multipath -l
3600d0230000000000e13955cc3757800 dm-1 WINSYS,SF2372
size=269G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 6:0:0:0 sdb 8:16 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 7:0:0:0 sdf 8:80 active ready running
The following example shows the output of a multipath -ll command.
# multipath -ll
3600d0230000000000e13955cc3757801 dm-10 WINSYS,SF2372
size=269G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=enabled
| `- 19:0:0:1 sdc 8:32 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 18:0:0:1 sdh 8:112 active ready running
3600d0230000000000e13955cc3757803 dm-2 WINSYS,SF2372
size=125G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 19:0:0:3 sde 8:64 active ready running
`- 18:0:0:3 sdj 8:144 active ready running
5.7. Multipath Command Options
Table 5.1. Useful multipath 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.
|
5.8. Determining Device Mapper Entries with the dmsetup Command
You can use the dmsetup command to find out which device mapper entries match the multipathed devices.
The following command displays all the device mapper devices and
their major and minor numbers. The 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
mpathd (253, 4)
mpathep1 (253, 12)
mpathfp1 (253, 11)
mpathb (253, 3)
mpathgp1 (253, 14)
mpathhp1 (253, 13)
mpatha (253, 2)
mpathh (253, 9)
mpathg (253, 8)
VolGroup00-LogVol01 (253, 1)
mpathf (253, 7)
VolGroup00-LogVol00 (253, 0)
mpathe (253, 6)
mpathbp1 (253, 10)
mpathd (253, 5)
5.9. Troubleshooting with the multipathd Interactive Console
The multipathd -k command is an interactive interface to the multipathd 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 CTRL-D to quit.
The multipathd 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
The following command sequence ensures that multipath has picked up any changes to the multipath.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
