Setup RAID on one of the failed Drive

In this tutorial we will going to learn the way to replace a failed drive in RAID setup on Linux system. First, of all we assume that we are having this type of raid setup.

Code:

root@hoststud [~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[2]
      4190208 blocks super 1.2 [2/2] [UU]

md2 : active raid1 sdb3[1] sda3[2]
      524156928 blocks super 1.2 [2/2] [UU]
      bitmap: 4/4 pages [16KB], 65536KB chunk

md1 : active raid1 sdb2[1] sda2[2]
      523712 blocks super 1.2 [2/2] [UU]

md3 : active raid1 sdb4[1] sda4[2]
      3377878848 blocks super 1.2 [2/2] [UU]
      bitmap: 0/26 pages [0KB], 65536KB chunk
unused devices: <none>

There are four partitions in total:
/dev/md0 - swap
/dev/md1 - /boot
/dev/md2 - /
/dev/md3 - /home

Now, let us assume /dev/sda got corrupted and failed the missing or defective drive is shown by [U_] and/or [_U]. If the RAID array is intact, it shows [UU].

Code:

root@hoststud [~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[2] (F)
      4190208 blocks super 1.2 [2/2] [U_]

md2 : active raid1 sdb3[1] sda3[2] (F)
      524156928 blocks super 1.2 [2/2] [U_]
      bitmap: 4/4 pages [16KB], 65536KB chunk

md1 : active raid1 sdb2[1] sda2[2] (F)
      523712 blocks super 1.2 [2/2] [U_]

md3 : active raid1 sdb4[1] sda4[2] (F)
      3377878848 blocks super 1.2 [2/2] [U_]
      bitmap: 0/26 pages [0KB], 65536KB chunk
unused devices: <none>

Now, we have to first remove the defective drive from the array before adding the new drive. It is quite simple and easily done by simple command given below:

Code:

# mdadm /dev/md0 -r /dev/sdb1
# mdadm /dev/md1 -r /dev/sdb2
# mdadm /dev/md2 -r /dev/sdb3
# mdadm /dev/md3 -r /dev/sdb4

Now, you have to contact your system administrator or datacenter support to replace the drive with new and confirm back. Once this is done then you have to prepare the new drive for the RAID.
Here, the condition is both drives in the RAID array need to have the exact same partitioning. For that we have to copy the partition table from sdb to sda

Code:

# sgdisk --backup=sdb_parttable_gpt.bak /dev/sdb
# sgdisk --load-backup=sdb_parttable_gpt.bak /dev/sda

Now, the sda drive then needs to be assigned a new random UUID:

Code:

# sgdisk -G /dev/sda

Then after, Integration of the new drive to RAID array

Code:

# mdadm /dev/md0 -a /dev/sda1
# mdadm /dev/md1 -a /dev/sda2
# mdadm /dev/md2 -a /dev/sda3
# mdadm /dev/md3 -a /dev/sda4

As the serial number of the sda disk changed after replacement we need to generate a new device-map with GRUB2:

Code:

# grub2-install /dev/sda

Now, you are done. Enjoy!

Setup RAID on one of the failed Drive

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