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Chapter 3. Configuring DM Multipath
You can set up DM Multipath with the mpathconf
utility. This utility creates or edits the /etc/multipath.conf
multipath configuration file based on the following scenarios:
-
If the
/etc/multipath.conf
file already exists, thempathconf
utility will edit it. -
If the
/etc/multipath.conf
file does not exist, thempathconf
utility will create the/etc/multipath.conf
file from scratch.
3.1. Checking for the device-mapper-multipath package
Before setting up DM Multipath on your system, ensure that your system is up-to-date and includes the device-mapper-multipath
package.
Procedure
Check if your system includes the
device-mapper-multipath
package:# rpm -q device-mapper-multipath device-mapper-multipath-current-package-version
If your system does not include the package, it prints the following:
package device-mapper-multipath is not installed
If your system does not include the package, install it by running the following command:
# dnf install device-mapper-multipath
3.2. Setting up basic failover configuration with DM Multipath
You can set up DM Multipath for a basic failover configuration and edit the /etc/multipath.conf
file before starting the multipathd daemon.
Prerequisites
- Administrative access.
Procedure
Enable and initialize the multipath configuration file:
# mpathconf --enable
Optional: Edit the
/etc/multipath.conf
file.Most default settings are already configured, including
path_grouping_policy
which is set tofailover
.Optional: The default naming format of multipath devices is set to
/dev/mapper/mpathn
format. If you prefer a different naming format:Configure DM Multipath to use the multipath device WWID as its name, instead of the mpath_n_ user-friendly naming scheme:
# mpathconf --enable --user_friendly_names n
Reload the configuration of the DM Multipath daemon:
# systemctl reload multipathd.service
Start the DM Multipath daemon:
# systemctl start multipathd.service
Verification
Confirm that the DM Multipath daemon is running without issues:
# systemctl status multipathd.service
Verify the naming format of multipath devices:
# ls /dev/mapper/
3.3. Ignoring local disks when generating multipath devices
Some machines have local SCSI cards for their internal disks and DM Multipath is not recommended for these devices. If you set the find_multipaths
configuration parameter to yes
, you do not have to disable multipathing on these devices.
If you do not set the find_multipaths
configuration parameter to yes
, you can use the following procedure to modify the DM Multipath configuration file to ignore the local disks when configuring multipath.
Procedure
Identify the internal disk using any known parameters such as the device’s model, path or vendor, and determine its WWID by using any one of the following options:
Display existing multipath devices:
# multipath -v2 -l mpatha (WDC_WD800JD-75MSA3_WD-WMAM9FU71040) dm-2 ATA,WDC WD800JD-75MS size=33 GB features="0" hwhandler="0" wp=rw `-+- policy='round-robin 0' prio=0 status=active |- 0:0:0:0 sda 8:0 active undef running
Display additional multipath devices that DM Multipath could create:
# multipath -v2 -d : mpatha (WDC_WD800JD-75MSA3_WD-WMAM9FU71040) dm-2 ATA,WDC WD800JD-75MS size=33 GB features="0" hwhandler="0" wp=undef `-+- policy='round-robin 0' prio=1 status=undef |- 0:0:0:0 sda 8:0 undef ready running
Display device information:
# multipathd show paths raw format "%d %w" | grep sda sda WDC_WD800JD-75MSA3_WD-WMAM9FU71040
In this example,
/dev/sda
is the internal disk and its WWID isWDC_WD800JD-75MSA3_WD-WMAM9FU71040
.
Edit the
blacklist
section of the/etc/multipath.conf
file to ignore this device, using its WWID attribute:blacklist { wwid WDC_WD800JD-75MSA3_WD-WMAM9FU71040 }
WarningAlthough you could identify the device using its
devnode
parameter, such assda
, it would not be a safe procedure, because/dev/sda
is not guaranteed to refer to the same device on reboot.Check for any configuration errors in the
/etc/multipath.conf
file:# multipath -t > /dev/null
To see the full report, do not discard the command output:
# multipath -t
-
If the disk is included in
initramfs
remake the initramfs. For more information see Configuring multipathing in initramfs. Reload the
/etc/multipath.conf
file by reconfiguring themultipathd
daemon:# systemctl reload multipathd
Multipath devices on top of local disks cannot be removed when in use. To ignore such device, stop all users of the device. For example, by unmounting any filesystem on top of it and deactivating any logical volumes using it. If this is not possible, you can reboot the system to remove the multipath device.
Verification
Verify that the internal disk is ignored and it is not displayed in the multipath output:
List the multipathed devices:
# multipath -v2 -l
List the additional devices that DM Multipath could create:
# multipath -v2 -d
Additional resources
-
multipath.conf(5)
man page
3.4. Configuring additional storage with DM Multipath
By default, DM Multipath includes built-in configurations for the most common storage arrays, which support DM Multipath. If your storage array does not already have a configuration, you can add one by editting the /etc/multipath.conf
file.
- NOTE
- Add additional storage devices during the initial configuration to align the setup with your anticipated needs. DM Multipath enables adding devices later for scalability or upgrades, but this approach may require adjusting configurations to ensuring compatibility.
Prerequisites
- Administrative access.
Procedure
View the default configuration value and supported devices:
# multipathd show config
Edit the
/etc/multipath.conf
file to set up your multipath configuration.Example 3.1. DM Multipath Configuration for HP OPEN-V Storage Device
# Set default configurations for all devices managed by DM Multipath defaults { # Enable user-friendly names for devices user_friendly_names yes } devices { # Define configuration for HP OPEN-V storage device { vendor "HP" pproduct "OPEN-V" no_path_retry 18 } }
- Save your changes and close the editor.
Update the multipath device list by scanning for new devices:
# multipath -r
Verification
Confirm that the multipath devices are recognized correctly:
# multipath -ll
3.5. Configuring multipathing in initramfs
Setting up multipathing in the initramfs
file system is essential for seamless storage functionality, particularly in scenarios requiring redundancy and load balancing. This setup guarantees that multipath devices are available early in the boot process, which is crucial for maintaining the integrity of the storage setup and preventing potential issues.
Prerequisites
- Administrative access.
- Configured DM multipath on your system.
Procedure
Rebuild the
initramfs
file system with the multipath configuration files:# dracut --force --add multipath
- NOTE
-
When using multipath in the
initramfs
and modifying its configuration files, remember to rebuild theinitramfs
for the changes to tale effect. If your root device employs multipath, thedracut
command will automatically include the multipath module in theinitramfs
.
Optional: If multipath in the
initramfs
is no longer necessary:Remove the multipath configuration file:
# rm /etc/dracut.conf.d/multipath.conf
Rebuild the
initramfs
with the added multipath configuration:# dracut --force --omit multipath
Verification
Check if multipath-related files and configurations are present:
# lsinitrd /path/to/initramfs.img -m | grep multipath
- NOTE
- While verefication steps provided can give you an indication of success, a final test boot-up is recommended to ensure that the configuration works as expected.
After the reboot, confirm that the multipath devices are recognized correctly:
# multipath -ll