mdadm: Add a hot-spare after failing a disk

Sun, 27 Jul 2014 21:46:33 +0000

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:

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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:

mdadm: Update md name

Thu, 10 Jan 2013 23:06:52 +0000

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mdadm --stop /dev/md127
mdadm --assemble /dev/md127 --name=charon:aggr0 --update=name
 /dev/sdb1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sda1

Mdadm on BAFM

mdadm: Add a hot-spare after failing a disk

mdadm: Update md name