Degraded RAID5 and no md superblock on one of remaining drive
- by ark1214
This is actually on a QNAP TS-509 NAS. The RAID is basically a Linux RAID.
The NAS was configured with RAID 5 with 5 drives (/md0 with /dev/sd[abcde]3). At some point, /dev/sde failed and drive was replaced. While rebuilding (and not completed), the NAS rebooted itself and /dev/sdc dropped out of the array. Now the array can't start because essentially 2 drives have dropped out. I disconnected /dev/sde and hoped that /md0 can resume in degraded mode, but no luck.. Further investigation shows that /dev/sdc3 has no md superblock. The data should be good since the array was unable to assemble after /dev/sdc dropped off.
All the searches I done showed how to reassemble the array assuming 1 bad drive. But I think I just need to restore the superblock on /dev/sdc3 and that should bring the array up to a degraded mode which will allow me to backup data and then proceed with rebuilding with adding /dev/sde.
Any help would be greatly appreciated.
mdstat does not show /dev/md0
# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath]
md5 : active raid1 sdd2[2](S) sdc2[3](S) sdb2[1] sda2[0]
530048 blocks [2/2] [UU]
md13 : active raid1 sdd4[3] sdc4[2] sdb4[1] sda4[0]
458880 blocks [5/4] [UUUU_]
bitmap: 40/57 pages [160KB], 4KB chunk
md9 : active raid1 sdd1[3] sdc1[2] sdb1[1] sda1[0]
530048 blocks [5/4] [UUUU_]
bitmap: 33/65 pages [132KB], 4KB chunk
mdadm show /dev/md0 is still there
# mdadm --examine --scan
ARRAY /dev/md9 level=raid1 num-devices=5 UUID=271bf0f7:faf1f2c2:967631a4:3c0fa888
ARRAY /dev/md5 level=raid1 num-devices=2 UUID=0d75de26:0759d153:5524b8ea:86a3ee0d
spares=2
ARRAY /dev/md0 level=raid5 num-devices=5 UUID=ce3e369b:4ff9ddd2:3639798a:e3889841
ARRAY /dev/md13 level=raid1 num-devices=5 UUID=7384c159:ea48a152:a1cdc8f2:c8d79a9c
With /dev/sde removed, here is the mdadm examine output showing sdc3 has no md superblock
# mdadm --examine /dev/sda3
/dev/sda3:
Magic : a92b4efc
Version : 00.90.00
UUID : ce3e369b:4ff9ddd2:3639798a:e3889841
Creation Time : Sat Dec 8 15:01:19 2012
Raid Level : raid5
Used Dev Size : 1463569600 (1395.77 GiB 1498.70 GB)
Array Size : 5854278400 (5583.08 GiB 5994.78 GB)
Raid Devices : 5
Total Devices : 4
Preferred Minor : 0
Update Time : Sat Dec 8 15:06:17 2012
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 1
Spare Devices : 0
Checksum : d9e9ff0e - correct
Events : 0.394
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 0 8 3 0 active sync /dev/sda3
0 0 8 3 0 active sync /dev/sda3
1 1 8 19 1 active sync /dev/sdb3
2 2 8 35 2 active sync /dev/sdc3
3 3 8 51 3 active sync /dev/sdd3
4 4 0 0 4 faulty removed
[~] # mdadm --examine /dev/sdb3
/dev/sdb3:
Magic : a92b4efc
Version : 00.90.00
UUID : ce3e369b:4ff9ddd2:3639798a:e3889841
Creation Time : Sat Dec 8 15:01:19 2012
Raid Level : raid5
Used Dev Size : 1463569600 (1395.77 GiB 1498.70 GB)
Array Size : 5854278400 (5583.08 GiB 5994.78 GB)
Raid Devices : 5
Total Devices : 4
Preferred Minor : 0
Update Time : Sat Dec 8 15:06:17 2012
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 1
Spare Devices : 0
Checksum : d9e9ff20 - correct
Events : 0.394
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 1 8 19 1 active sync /dev/sdb3
0 0 8 3 0 active sync /dev/sda3
1 1 8 19 1 active sync /dev/sdb3
2 2 8 35 2 active sync /dev/sdc3
3 3 8 51 3 active sync /dev/sdd3
4 4 0 0 4 faulty removed
[~] # mdadm --examine /dev/sdc3
mdadm: No md superblock detected on /dev/sdc3.
[~] # mdadm --examine /dev/sdd3
/dev/sdd3:
Magic : a92b4efc
Version : 00.90.00
UUID : ce3e369b:4ff9ddd2:3639798a:e3889841
Creation Time : Sat Dec 8 15:01:19 2012
Raid Level : raid5
Used Dev Size : 1463569600 (1395.77 GiB 1498.70 GB)
Array Size : 5854278400 (5583.08 GiB 5994.78 GB)
Raid Devices : 5
Total Devices : 4
Preferred Minor : 0
Update Time : Sat Dec 8 15:06:17 2012
State : active
Active Devices : 4
Working Devices : 4
Failed Devices : 1
Spare Devices : 0
Checksum : d9e9ff44 - correct
Events : 0.394
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 3 8 51 3 active sync /dev/sdd3
0 0 8 3 0 active sync /dev/sda3
1 1 8 19 1 active sync /dev/sdb3
2 2 8 35 2 active sync /dev/sdc3
3 3 8 51 3 active sync /dev/sdd3
4 4 0 0 4 faulty removed
fdisk output shows /dev/sdc3 partition is still there.
[~] # fdisk -l
Disk /dev/sdx: 128 MB, 128057344 bytes
8 heads, 32 sectors/track, 977 cylinders
Units = cylinders of 256 * 512 = 131072 bytes
Device Boot Start End Blocks Id System
/dev/sdx1 1 8 1008 83 Linux
/dev/sdx2 9 440 55296 83 Linux
/dev/sdx3 441 872 55296 83 Linux
/dev/sdx4 873 977 13440 5 Extended
/dev/sdx5 873 913 5232 83 Linux
/dev/sdx6 914 977 8176 83 Linux
Disk /dev/sda: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 66 530113+ 83 Linux
/dev/sda2 67 132 530145 82 Linux swap / Solaris
/dev/sda3 133 182338 1463569695 83 Linux
/dev/sda4 182339 182400 498015 83 Linux
Disk /dev/sda4: 469 MB, 469893120 bytes
2 heads, 4 sectors/track, 114720 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk /dev/sda4 doesn't contain a valid partition table
Disk /dev/sdb: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 * 1 66 530113+ 83 Linux
/dev/sdb2 67 132 530145 82 Linux swap / Solaris
/dev/sdb3 133 182338 1463569695 83 Linux
/dev/sdb4 182339 182400 498015 83 Linux
Disk /dev/sdc: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdc1 1 66 530125 83 Linux
/dev/sdc2 67 132 530142 83 Linux
/dev/sdc3 133 182338 1463569693 83 Linux
/dev/sdc4 182339 182400 498012 83 Linux
Disk /dev/sdd: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdd1 1 66 530125 83 Linux
/dev/sdd2 67 132 530142 83 Linux
/dev/sdd3 133 243138 1951945693 83 Linux
/dev/sdd4 243139 243200 498012 83 Linux
Disk /dev/md9: 542 MB, 542769152 bytes
2 heads, 4 sectors/track, 132512 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk /dev/md9 doesn't contain a valid partition table
Disk /dev/md5: 542 MB, 542769152 bytes
2 heads, 4 sectors/track, 132512 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk /dev/md5 doesn't contain a valid partition table