> [root@livecd ~]# mdadm --misc -E /dev/md0
> mdadm: No md superblock detected on /dev/md0.
> [root@livecd ~]# mdadm --misc -Q /dev/md0
> /dev/md0: is an md device which is not active
> /dev/md0: No md super block found, not an md component.
> [root@livecd ~]# mdadm --misc -D /dev/md0
> mdadm: md device /dev/md0 does not appear to be active.
I could fix the issue.
Since the information on internet is a bit messy and scary here is a
summary of the problem and of the solution, for future reference:
## PROBLEM
Due to some failure related to suspend the RAID5 array became inconsistent.
The symptom was that the superblock (which allow auto-configuration of
the RAID array) was not recognized.
But the underlying member partitions were still recognized as per the
following command:
> [root@livecd ~]# mdadm -E /dev/sd*3
which provided details about their states
## SOLUTION
(detailed output of the commands at the end of the post)
# Assemble the array with force option
mdadm -v --assemble --force /dev/md0 /dev/sd{a,b,c,d}3
# NOTE: assembling without force option was not enough
[root@livecd ~]# mdadm -v --assemble /dev/md0 /dev/sd{a,b,c,d}3
...
mdadm: /dev/md0 assembled from 2 drives - not enough to start the
array while not clean - consider --force.
# Check state
mdadm -D /dev/md0
...
Number Major Minor RaidDevice State
0 8 3 0 active sync /dev/sda3
1 0 0 1 removed
2 8 51 2 active sync /dev/sdd3
# Add missing partitions to the array
mdadm /dev/md0 -a /dev/sdb3
mdadm /dev/md0 -a /dev/sdc3
# Check that it is now OK
mdadm -D /dev/md0
...
Number Major Minor RaidDevice State
0 8 3 0 active sync /dev/sda3
1 8 19 1 spare rebuilding /dev/sdb3
2 8 51 2 active sync /dev/sdd3
3 8 35 - spare /dev/sdc3
# and watch it rebuild:
...
Rebuild Status : 3% complete
Many thanks to the CentOS LiveCD team, they saved the day.
Cheers,
Mathieu
## DETAILED OUTPUT
[root@livecd ~]# mdadm -v --assemble --force /dev/md0 /dev/sd{a,b,c,d}3
mdadm: looking for devices for /dev/md0
mdadm: /dev/sda3 is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sdb3 is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sdc3 is identified as a member of /dev/md0, slot 1.
mdadm: /dev/sdd3 is identified as a member of /dev/md0, slot 2.
mdadm: added /dev/sdc3 to /dev/md0 as 1
mdadm: added /dev/sdd3 to /dev/md0 as 2
mdadm: added /dev/sda3 to /dev/md0 as 0
mdadm: /dev/md0 has been started with 2 drives (out of 3).
[root@livecd ~]# mdadm -D /dev/md0
/dev/md0:
Version : 0.90
Creation Time : Tue Dec 1 12:01:05 2009
Raid Level : raid5
Array Size : 409592832 (390.62 GiB 419.42 GB)
Used Dev Size : 204796416 (195.31 GiB 209.71 GB)
Raid Devices : 3
Total Devices : 2
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Wed Aug 17 14:47:36 2011
State : clean, degraded
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 256K
UUID : 7533411a:f066a145:1e89d48e:1a8374a3
Events : 0.38857
Number Major Minor RaidDevice State
0 8 3 0 active sync /dev/sda3
1 0 0 1 removed
2 8 51 2 active sync /dev/sdd3
[root@livecd ~]# mdadm /dev/md0 -a /dev/sdb3
mdadm: re-added /dev/sdb3
[root@livecd ~]# mdadm /dev/md0 -a /dev/sdc3
mdadm: added /dev/sdc3
[root@livecd ~]# mdadm -D /dev/md0
/dev/md0:
Version : 0.90
Creation Time : Tue Dec 1 12:01:05 2009
Raid Level : raid5
Array Size : 409592832 (390.62 GiB 419.42 GB)
Used Dev Size : 204796416 (195.31 GiB 209.71 GB)
Raid Devices : 3
Total Devices : 4
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Wed Aug 17 14:47:36 2011
State : clean, degraded, recovering
Active Devices : 2
Working Devices : 4
Failed Devices : 0
Spare Devices : 2
Layout : left-symmetric
Chunk Size : 256K
Rebuild Status : 0% complete
UUID : 7533411a:f066a145:1e89d48e:1a8374a3
Events : 0.38857
Number Major Minor RaidDevice State
0 8 3 0 active sync /dev/sda3
1 8 19 1 spare rebuilding /dev/sdb3
2 8 51 2 active sync /dev/sdd3
3 8 35 - spare /dev/sdc3
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