Software RAID is becoming very common with Linux based workstation and server environments. The following sections in this blog post will help provide guidance on viewing the current software RAID health (mdadm), as well as removing and re-adding drives for software RAID maintenance as needed to keep the software RAID devices healthy.


Viewing a software RAID health, determining status, if a drive needs to be replaced/re-added


Sample output for Two 256GB SSD with RAID1

Instead of the string [UU] you will see [U_] if you have a degraded RAID1 array

cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]

md0  :   active raid1 sda1[0] sdb1[1]

     194368 blocks super 1.2 [2/2] [UU]

md1   :   active raid1 sda2[0] sdb2[1]

      9757568 blocks super 1.2 [2/2] [UU]

md2   :   active raid1 sda3[2] sdb3[1]

      239966016 blocks super 1.2 [2/2] [UU]


Re-adding a drive to a MDADM array

If there is any RAID drive/partition is missing, you need to re-adding the drive to MDADM array.

Sample output of adding a drive(partition) sdb1 to the RAID(md0)

mdadam –add /dev/md0 /dev/sdb1


During the synchronization the output will look like the following:

cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10]

md0 : active raid1 sda1[0] sdb1[1]

194368 blocks [2/1] [U_]

[=>……………….]  recovery =  9.9% (19242/194368) finish=1.1min speed=127535K/sec


Removing a drive from an MDADM array

  1. Unmount the array that containing the drive (ie sda1)
umount /dev/md0


  1. Shut down the array that containing the drive sda1
mdadm –stop /dev/md0


  1. Remove the drive from the array
mdadm –manage /dev/md0 –remove /dev/sda1

mdadm: hot removed /dev/sda1


  1. Zero the Superblock
mdadm –zero-superblock /dev/sda1