Configuring Linux Multipathing

You must configure the everRun system to use Linux multipathing if the system includes external storage. Multipathing enables the system to provide multiple paths to external storage systems. When everRun software is installed, the device-mapper-multipath package is also installed. However, everRun software does not configure multipath. Follow the instructions provided in the CentOs documentation to configure multipath. See https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/DM_Multipath/.

For everRun software to function properly, you must perform the required procedures below on both nodes after configuring multipath.

To set path_selector, blacklist drbd, and then set no_path_retry

1. Set up the initial /etc/multipath.conf file by issuing the following command:

   mpathconf --enable --user_friendly_names y --find_multipaths y --with_multipathd y

2. Edit the /etc/multipath.conf file, making the following changes:

   1. Add the entry path_selector "round-robin 0" to the defaults section, as in the following example.

      ## Use user friendly names, instead of using WWIDs as names.
      defaults {
      user_friendly_names yes
      find_multipaths yes
      path_selector "round-robin 0"
      }

   2. Add or modify the blacklist entry (at the end of the multipathd file) to include drbd, so that the entry is identical to the following:

      blacklist {
      devnode "^(ram|zram|raw|loop|fd|md|dm-|sr|scd|st|drbd)[0-9]*"
      }

   3. Add the following devices entry just below the blacklist line:

      devices {
      device {
      vendor "DGC"
      product "VRAID"
      no_path_retry "0"
      }
      }
      Note: The example shown above is for an EMC storage array. The values for vendor and product vary according to the manufacturer and model of your storage array.

   4. Save the /etc/multipath.conf file.

3. To restart multipathd and to ensure that it can start at boot time and is functioning properly, issue the following commands in the order given:

   systemctl restart multipathd
   systemctl enable multipathd
   systemctl status multipathd

4. To verify that no_path_retry is set to fail, issue the following command:

   multipathd show config

   The following sample lines appear at the end of output for an EMC VNX configuration:

   device {
   vendor "DGC"
   product "VRAID"
   product_blacklist "LUNZ"
   path_grouping_policy "group_by_prio"
   path_checker "emc_clariion"
   features "0"
   hardware_handler "1 emc"
   prio "emc"
   failback immediate
   rr_weight "uniform"
   no_path_retry "fail"
   retain_attached_hw_handler yes
   detect_prio yes
   }

Related Topics

External Storage

Managing External Storage