Use IQN string as device name in Linux with multipathing

[aherbert23]

Sometimes it's difficult to know which device is which under Linux. Even more difficult when adding in the multipathing layer. This can all be remedied with a custom script and a few modifications to the multipath.conf file. The multipath.conf file has a parameter for creating a custom callout script for naming and grouping devices. The default is to use the SCSI ID of the device. This is how multipathd knows which devices should be grouped together. This custom script will use the unique IQN string of the device which will make identifying the device later through device mapper much easier.

The first step is to create a file /usr/local/sbin/iscsi_id.sh with the following content and set it as executable.

#!/bin/bash

ls -l /dev/disk/by-path/ | egrep iscsi | egrep "$1$" | sed -e 's/.*:\([a-z0-9.:-]*\).*/\1/'

Then modify the /etc/multipath.conf file with the getuid_callout variable on line 32 to point to the new script.

defaults {
  path_grouping_policy multibus
  rr_min_io 20
}

blacklist {
  devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
  devnode "^hd[a-z][[0-9]*]"
  device {
    vendor "*"
    product "*"
  }
}

blacklist_exceptions {
  device {
    vendor "Nimble"
    product "Server"
  }
}

devices {
  device {
    vendor "Nimble"
    product "Server"
    path_selector "round-robin 0"
    path_grouping_policy group_by_serial
    path_checker tur
    rr_min_io 20
    failback manual
    rr_weight priorities
    getuid_callout "/usr/local/sbin/iscsi_id.sh %n"
  }
}

Once these changes are in place listing /dev/mapper makes the time spent making this modification worth all the effort.

ls -l /dev/mapper/
total 0
crw------- 1 root root 10, 236 Dec 17 08:48 control
lrwxrwxrwx 1 root root       7 Dec 17 13:28 mysql-clone-v16da9ef36265f874.000001dd.74bf6687-lun-0 -> ../dm-2
lrwxrwxrwx 1 root root       7 Dec 17 13:28 mysql-clone-v16da9ef36265f874.000001dd.74bf6687-lun-0-part1 -> ../dm-3