Linux Software Raid (MdAdm)

Recover a standalone disk from RAID1 failure

# Connect disk, suppose it get recognized as /dev/sdb

# Array it's probably assembled automatically as `/dev/mdNNN`, but _inactive_
root@motoko:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md125 : inactive sdb6[0](S)
  953321472 blocks super 1.2

md126 : inactive sdb1[0](S)
  19529728 blocks super 1.2

md127 : inactive sdb5[1](S)
  3905528 blocks super 1.2

root@motoko:~# mdadm --stop /dev/md125

root@motoko:~# mdadm --assemble --force /dev/md0 /dev/sdb6`
mdadm: /dev/md0 has been started with 1 drive (out of 2).

root@motoko:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb6[0]
      953321336 blocks super 1.2 [2/1] [U_]

unused devices: <none>

root@motoko:~# mkdir /mnt/recovery
root@motoko:~# mount /dev/md0 /mnt/recovery

# if fails try also
root@motoko:~# fsck -p /dev/md0