mdadm: Add a hot-spare after failing a disk
Once the disk is failed (or is actually defective), mdadm will automatically remove it from the RAID. After that, you’ll either have to add the disk back as a data disk or as a hot-spare (which was in my case). Now, here’s after the rebuild for the failed disk started: 1 2 3 4 5 6 7 8 root:(charon.ka.heimdaheim.de) PWD:~ Sun Jul 27, 23:40:35 [0] > cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md127 : active raid5 sdi1[0] sdh1[6] sdj1[7] sdk1[8] sdf1[9] sdb1[5] sde1[4] sdd1[2] sdc1[1] 15626121216 blocks super 1.2 level 5, 512k chunk, algorithm 2 [9/8] [UUUUU_UUU] [===================>.] recovery = 97.9% (1913176308/1953265152) finish=12.3min speed=53936K/sec unused devices: <none> In order to add the replaced disk back to the RAID, you’ll have to prepare a partition for it (see this post for more details). After that, it’s a simple call with mdadm to re-add the hot-spare: ...