Chapter 3. Configuring DM Multipath

Procedure

1. 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

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

   # yum install device-mapper-multipath

Procedure

1. Enable and initialize the multipath configuration file:

   # 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:

      # mpathconf --enable --user_friendly_names n

   2. Reload the configuration of the DM Multipath daemon:

      # systemctl reload multipathd.service

4. Start the DM Multipath daemon:

   # 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:

     # 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 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:

   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:

   # multipath -t > /dev/null

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

   # multipath -t

4. If the disk is included in initramfs remake the initramfs. For more information see Configuring multipathing in initramfs.

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

   # 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:

     # multipath -v2 -l

   • List the additional devices that DM Multipath could create:

     # multipath -v2 -d

Procedure

1. View the default configuration value and supported devices:

   # 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

   # 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:

   # multipath -r

Procedure

1. 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 the initramfs for the changes to tale 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:

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

   2. Rebuild the initramfs with the added multipath configuration:

      # dracut --force --omit multipath