I learned recently that software RAID devices under Linux can have friendly names. I had never specified a name when creating arrays.

I’ve been recently updating my fileserver to RHEL 8 and working with the original array I created in 2015 and documented in my post: RAID 6 and LVM. In the original version of that post, I did not specify a name.

I’ve found that naming my RAID volumes has a great benefit when reinstalling the system via Kickstart, which I’ll write about more in detail later.

So, my RAID volumes are unnamed….how do I give them a name?

First, let’s look at our RAID volume using the mdadm --detail command:

# mdadm --detail /dev/md200
/dev/md200:
           Version : 1.2
     Creation Time : Thu Sep 24 17:47:54 2015
        Raid Level : raid6
        Array Size : 3906521088 (3.64 TiB 4.00 TB)
     Used Dev Size : 976630272 (931.39 GiB 1000.07 GB)
      Raid Devices : 6
     Total Devices : 6
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Thu Jun  9 03:11:45 2022
             State : clean 
    Active Devices : 6
   Working Devices : 6
    Failed Devices : 0
     Spare Devices : 0

            Layout : left-symmetric
        Chunk Size : 512K

Consistency Policy : bitmap

              Name : 200
              UUID : 6d90c19a:9812e659:6854747b:a89f1280
            Events : 34710

    Number   Major   Minor   RaidDevice State
       0       8       97        0      active sync   /dev/sdg1
       1       8       17        1      active sync   /dev/sdb1
       2       8       49        2      active sync   /dev/sdd1
       3       8      113        3      active sync   /dev/sdh1
       4       8       65        4      active sync   /dev/sde1
       5       8       81        5      active sync   /dev/sdf1

Above, there is a name field, but it’s not really a human name, just 200. This is really just the /dev/md### number.

Renaming is a relatively simple operation, but it can’t be done live.

In my setup, I have a LVM Volume Group called galadriel. I want to rename my RAID device to also be galadriel to match.

  1. Run mdadm --detail and save the output somewhere for reference.

  2. Unmount all volumes related to either the RAID device or volume group using the RAID.

  3. Stop the volume group. -a n deactivates the volume group.

     vgchange -a n galadriel

  4. Stop the md device using mdadm

     sudo mdadm --stop /dev/md200

  5. Reassemble with new name. This reassembles the drive with the --name. The device names can be gleaned from the output of `mdadm –detail.

     sudo mdadm --assemble --update=name --name=galadriel /dev/md200 /dev/sdg1 /dev/sdb1 /dev/sdd1 /dev/sdh1 /dev/sde1 /dev/sdf1

  6. Reactivate the volume group

     vgchange -a y galadriel

  7. Check that everthing is OK, by looking at /dev/mdstat, comparing new output of mdadm --detail, vgs, and lvs.

     # cat /proc/mdstat
 md200 : active raid6 sdf1[1] sdh1[2] sdd1[3] sda1[4] sdc1[0] sdb1[5]
       3906521088 blocks super 1.2 level 6, 512k chunk, algorithm 2 [6/6] [UUUUUU]
       bitmap: 0/8 pages [0KB], 65536KB chunk

  8. It may be required to update /etc/mdadm.conf. In RHEL7+, the UUID is used, so only the dev path may need to be updated:

    # cat /etc/mdadm.conf
    
   ### Snippet of relevant line:
ARRAY /dev/md/galadriel level=raid6 num-devices=6 UUID=6d90c19a:9812e659:6854747b:a89f1280