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The last three nights, one of my USB controllers has gone offline in the middle of the night, knocking 4 of my 8 disks offline. The first two times, I was able to get it working again with mdadm -A /dev/md0 -f /dev/sd[hgeflkji]. I tried that this morning and it's not working. Any ideas?

[root@dl380g5 ~]# mdadm --examine /dev/sd[efghijkl] |egrep 'Event'
     Events : 37261
     Events : 37261
     Events : 37261
     Events : 37261
     Events : 37249
     Events : 37248
     Events : 37249
     Events : 37248
[root@dl380g5 ~]# mdadm -A /dev/md0 --force -v /dev/sd[hgeflkji]
mdadm: looking for devices for /dev/md0
mdadm: /dev/sde is identified as a member of /dev/md0, slot 2.
mdadm: /dev/sdf is identified as a member of /dev/md0, slot 3.
mdadm: /dev/sdg is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sdh is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sdi is identified as a member of /dev/md0, slot 7.
mdadm: /dev/sdj is identified as a member of /dev/md0, slot 6.
mdadm: /dev/sdk is identified as a member of /dev/md0, slot 5.
mdadm: /dev/sdl is identified as a member of /dev/md0, slot 4.
mdadm: added /dev/sdg to /dev/md0 as 1
mdadm: added /dev/sde to /dev/md0 as 2
mdadm: added /dev/sdf to /dev/md0 as 3
mdadm: added /dev/sdl to /dev/md0 as 4 (possibly out of date)
mdadm: added /dev/sdk to /dev/md0 as 5 (possibly out of date)
mdadm: added /dev/sdj to /dev/md0 as 6 (possibly out of date)
mdadm: added /dev/sdi to /dev/md0 as 7 (possibly out of date)
mdadm: added /dev/sdh to /dev/md0 as 0
mdadm: /dev/md0 assembled from 4 drives - not enough to start the array.
[root@dl380g5 ~]# mdadm --detail /dev/md0
mdadm: cannot open /dev/md0: No such file or directory
[root@dl380g5 ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
unused devices: <none>
[root@dl380g5 ~]# cat /etc/mdadm.conf
ARRAY /dev/md0 metadata=1.2 name=fs2.internal.xxxxxxxxx.xxx:0 UUID=a3521a6d:596057f0:87205aac:3aab2ef2
[root@dl380g5 ~]#
  • Note that RAID5 can survive the loss of a single element. You lost four. I don't know for sure, but I suspect it'll be time to restore from backup. – ChrisInEdmonton Mar 12 '15 at 13:37
  • Please read before responding. As I stated, it is possible and has been done. This procedure is well documented, but doesn't seem to be working today. – Kevin Reichhart Mar 12 '15 at 14:24
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In my experience mdadm will force the event counts to update. I see cases like this often. Be sure you are using the latest mdadm version.

If all else fails you can perform an mdadm --create but you must be 100% sure to use the correct mdadm parameters or you will be digging a deeper hole.

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