Code:
tunafish:/home/cwilliams# mdadm --remove /dev/md0 /dev/sdb4
mdadm: hot removed /dev/sdb4
tunafish:/home/cwilliams# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda3[0] sdb3[1]
19534976 blocks [2/2] [UU]
md1 : active raid1 sda4[0]
135275264 blocks [2/1] [U_]
unused devices: <none>
tunafish:/home/cwilliams# mdadm --re-add /dev/md1 /dev/sdb4
mdadm: added /dev/sdb4
tunafish:/home/cwilliams# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda3[0] sdb3[1]
19534976 blocks [2/2] [UU]
md1 : active raid1 sdb4[2] sda4[0]
135275264 blocks [2/1] [U_]
[>....................] recovery = 0.1% (259200/135275264) finish=34.7min speed=64800K/sec