Chapter 3. Configuring DM Multipath

Procedure

1. Check if your system includes the device-mapper-multipath package:

   Copy to Clipboard Toggle word wrap

   # rpm -q device-mapper-multipath
   device-mapper-multipath-current-package-version

   If your system does not include the package, it prints the following:

   Copy to Clipboard Toggle word wrap

   package device-mapper-multipath is not installed

2. If your system does not include the package, install it by running the following command:

   Copy to Clipboard Toggle word wrap

   # yum install device-mapper-multipath

Procedure

1. Enable and initialize the multipath configuration file:

   Copy to Clipboard Toggle word wrap

   # mpathconf --enable

2. Optional: Edit the /etc/multipath.conf file.

   Most default settings are already configured, including path_grouping_policy which is set to failover.

3. Optional: The default naming format of multipath devices is set to /dev/mapper/mpathn format. If you prefer a different naming format:

   1. Configure DM Multipath to use the multipath device WWID as its name, instead of the mpath_n_ user-friendly naming scheme:

      Copy to Clipboard Toggle word wrap

      # mpathconf --enable --user_friendly_names n

   2. Reload the configuration of the DM Multipath daemon:

      Copy to Clipboard Toggle word wrap

      # systemctl reload multipathd.service

4. Start the DM Multipath daemon:

   Copy to Clipboard Toggle word wrap

   # systemctl start multipathd.service

Procedure

1. 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:

     Copy to Clipboard Toggle word wrap

     # 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:

     Copy to Clipboard Toggle word wrap

     # 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:

     Copy to Clipboard Toggle word wrap

     # 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 is WDC_WD800JD-75MSA3_WD-WMAM9FU71040.

2. Edit the blacklist section of the /etc/multipath.conf file to ignore this device, using its WWID attribute:

   Copy to Clipboard Toggle word wrap

   blacklist {
         wwid WDC_WD800JD-75MSA3_WD-WMAM9FU71040
   }

   Warning

   Although you could identify the device using its devnode parameter, such as sda, it would not be a safe procedure, because /dev/sda is not guaranteed to refer to the same device on reboot.

3. Check for any configuration errors in the /etc/multipath.conf file:

   Copy to Clipboard Toggle word wrap

   # multipath -t > /dev/null

   To see the full report, do not discard the command output:

   Copy to Clipboard Toggle word wrap

   # multipath -t

4. Remake the initramfs if the disk is included in initramfs. For more information, see Configuring multipathing in initramfs.

5. Reload the /etc/multipath.conf file by reconfiguring the multipathd daemon:

   Copy to Clipboard Toggle word wrap

   # systemctl reload multipathd

Verification

1. Verify that the internal disk is ignored and it is not displayed in the multipath output:

   • List the multipathed devices:

     Copy to Clipboard Toggle word wrap

     # multipath -v2 -l

   • List the additional devices that DM Multipath could create:

     Copy to Clipboard Toggle word wrap

     # multipath -v2 -d

Procedure

1. View the default configuration value and supported devices:

   Copy to Clipboard Toggle word wrap

   # multipathd show config

2. Edit the /etc/multipath.conf file to set up your multipath configuration.

   Example 3.1. DM Multipath Configuration for HP OPEN-V Storage Device

   Copy to Clipboard Toggle word wrap

   # 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
       }
   }

3. Save your changes and close the editor.

4. Update the multipath device list by scanning for new devices:

   Copy to Clipboard Toggle word wrap

   # multipath -r

Procedure

1. Rebuild the initramfs file system with the multipath configuration files:

   Copy to Clipboard Toggle word wrap

   # dracut --force --add multipath

   Note

   When using multipath in the initramfs and modifying its configuration files, remember to rebuild the initramfs for the changes to take effect. If your root device employs multipath, the dracut command will automatically include the multipath module in the initramfs.

2. Optional: If multipath in the initramfs is no longer necessary:

   1. Remove the multipath configuration file:

      Copy to Clipboard Toggle word wrap

      # rm /etc/dracut.conf.d/multipath.conf

   2. Rebuild the initramfs with the added multipath configuration:

      Copy to Clipboard Toggle word wrap

      # dracut --force --omit multipath