I've just moved house which involved dismantling my server and re-connecting it. Since doing so, one of my MDADM RAID5 arrays is appearing as inactive:
root@mserver:/tmp# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
md1 : active raid5 sdc1[1] sdh1[2] sdg1[0]
3907023872 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
md0 : inactive sdd1[0](S) sdf1[3](S) sde1[2](S) sdb1[1](S)
3907039744 blocks
unused devices:
It looks to me as though it's found all of the disks but for some reason doesn't want to use them.
So what do the (S) labels mean and how can I tell MDADM to start using the array again?
[Edit] I just tried stopping and assembling the array with -v:
root@mserver:~# mdadm --stop /dev/md0
mdadm: stopped /dev/md0
root@mserver:~# mdadm --assemble --scan -v
mdadm: /dev/sde1 is identified as a member of /dev/md0, slot 2.
mdadm: /dev/sdf1 is identified as a member of /dev/md0, slot 3.
mdadm: /dev/sdd1 is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sdb1 is identified as a member of /dev/md0, slot 1.
mdadm: added /dev/sdd1 to /dev/md0 as 0 (possibly out of date)
mdadm: added /dev/sdb1 to /dev/md0 as 1 (possibly out of date)
mdadm: added /dev/sdf1 to /dev/md0 as 3 (possibly out of date)
mdadm: added /dev/sde1 to /dev/md0 as 2
mdadm: /dev/md0 assembled from 1 drive - not enough to start the array.
..and entering cat /proc/mdstat looks no different.
[Edit2] Not sure if it helps but this is the result of examining each disk:
root@mserver:~# mdadm --examine /dev/sdb1
/dev/sdb1:
Magic : a92b4efc
Version : 0.90.00
UUID : 2f331560:fc85feff:5457a8c1:6e047c67 (local to host mserver)
Creation Time : Sun Feb 1 20:53:39 2009
Raid Level : raid5
Used Dev Size : 976759936 (931.51 GiB 1000.20 GB)
Array Size : 2930279808 (2794.53 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 0
Update Time : Sat Apr 20 13:22:27 2013
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Checksum : 6c8f71a3 - correct
Events : 955190
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 1 8 17 1 active sync /dev/sdb1
0 0 8 113 0 active sync /dev/sdh1
1 1 8 17 1 active sync /dev/sdb1
2 2 8 97 2 active sync /dev/sdg1
3 3 8 33 3 active sync /dev/sdc1
root@mserver:~# mdadm --examine /dev/sdd1
/dev/sdd1:
Magic : a92b4efc
Version : 0.90.00
UUID : 2f331560:fc85feff:5457a8c1:6e047c67 (local to host mserver)
Creation Time : Sun Feb 1 20:53:39 2009
Raid Level : raid5
Used Dev Size : 976759936 (931.51 GiB 1000.20 GB)
Array Size : 2930279808 (2794.53 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 2
Preferred Minor : 0
Update Time : Sat Apr 20 18:37:23 2013
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 2
Spare Devices : 0
Checksum : 6c812869 - correct
Events : 955205
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 0 8 113 0 active sync /dev/sdh1
0 0 8 113 0 active sync /dev/sdh1
1 1 0 0 1 faulty removed
2 2 8 97 2 active sync /dev/sdg1
3 3 0 0 3 faulty removed
root@mserver:~# mdadm --examine /dev/sde1
/dev/sde1:
Magic : a92b4efc
Version : 0.90.00
UUID : 2f331560:fc85feff:5457a8c1:6e047c67 (local to host mserver)
Creation Time : Sun Feb 1 20:53:39 2009
Raid Level : raid5
Used Dev Size : 976759936 (931.51 GiB 1000.20 GB)
Array Size : 2930279808 (2794.53 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 2
Preferred Minor : 0
Update Time : Sun Apr 21 14:00:43 2013
State : clean
Active Devices : 1
Working Devices : 1
Failed Devices : 2
Spare Devices : 0
Checksum : 6c90cc70 - correct
Events : 955219
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 2 8 97 2 active sync /dev/sdg1
0 0 0 0 0 removed
1 1 0 0 1 faulty removed
2 2 8 97 2 active sync /dev/sdg1
3 3 0 0 3 faulty removed
root@mserver:~# mdadm --examine /dev/sdf1
/dev/sdf1:
Magic : a92b4efc
Version : 0.90.00
UUID : 2f331560:fc85feff:5457a8c1:6e047c67 (local to host mserver)
Creation Time : Sun Feb 1 20:53:39 2009
Raid Level : raid5
Used Dev Size : 976759936 (931.51 GiB 1000.20 GB)
Array Size : 2930279808 (2794.53 GiB 3000.61 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 0
Update Time : Sat Apr 20 13:22:27 2013
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Checksum : 6c8f71b7 - correct
Events : 955190
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 3 8 33 3 active sync /dev/sdc1
0 0 8 113 0 active sync /dev/sdh1
1 1 8 17 1 active sync /dev/sdb1
2 2 8 97 2 active sync /dev/sdg1
3 3 8 33 3 active sync /dev/sdc1
I have some notes which suggest the drives were originally assembled as follows:
md0 : active raid5 sdb1[1] sdc1[3] sdh1[0] sdg1[2]
2930279808 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]
[Edit3]
Looking through the log it looks like the following happened (based on the Update Time in the --examine results):
- sdb and sdf were knocked out some time after 13:22 on the 20th
- sdd was knocked out some time after 18:37 on the 20th
- the server was shut down some time after 14:00 on the 1st
Given that two disks went down (apparently) simultaneously I think it should be reasonably safe to assume the array wouldn't have been written to after that point(?) and so it should be relatively safe to force it to re-instate in the correct order? What's the safest command to do that with and is there a way to do it without writing any changes?
Answer
The S labels means the disk is regarded as "spare". You should try stopping and re-starting the array:
mdadm --stop /dev/md0
mdadm --assemble --scan
to re-assemble the array and if that doesn't work, you may need to update your mdadm.conf, see for example this question for details on how to do that.
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