Current state of RAID array:
$ cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md125 : active raid1 sdf4[1] sde4[0] sdg4[2]
1922130944 blocks super 1.2 [3/3] [UUU]
unused devices: <none>
Modify RAID array /dev/md125
:
# mark disk as failed and remove (`sdg4` in this example)
mdadm --fail /dev/md125 /dev/sdg4
mdadm --remove /dev/md125 /dev/sdg4
# shrink to new size
mdadm --grow --raid-devices=2 /dev/md125
Verify:
$ cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md125 : active raid1 sdf4[1] sde4[0]
1922130944 blocks super 1.2 [2/2] [UU]
unused devices: <none>