I've got a server with a five-disk RAID-6 array. Last night, power to
the server went out, and when I powered it back up, one of the disks
failed. During bootup, the RAID array was assembled as an inactive
four-disk RAID-0 array with four spares rather than the expected
degraded RAID-6, and manually assembling the array doesn't give a
different result. Any idea how I can get my array back? There
doesn't appear to be anything wrong with the four remaining disks, it
simply isn't working.
Steps I used to manually assemble the array:
# mdadm --stop /dev/md2
# mdadm --assemble --verbose /dev/md2 /dev/sd[abcd]
mdadm: looking for devices for /dev/md2
mdadm: /dev/sda is identified as a member of /dev/md2, slot 1.
mdadm: /dev/sdb is identified as a member of /dev/md2, slot 0.
mdadm: /dev/sdc is identified as a member of /dev/md2, slot 3.
mdadm: /dev/sdd is identified as a member of /dev/md2, slot 4.
mdadm: added /dev/sda to /dev/md2 as 1
mdadm: no uptodate device for slot 2 of /dev/md2
mdadm: added /dev/sdc to /dev/md2 as 3
mdadm: added /dev/sdd to /dev/md2 as 4
mdadm: added /dev/sdb to /dev/md2 as 0
mdadm: /dev/md2 assembled from 4 drives - need all 5 to start it (use
--run to insist).
The results of the above steps:
# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md2 : inactive sdc[5](S) sdd[7](S) sda[9](S) sdb[8](S)
11721062240 blocks super 1.2
unused devices: <none>
# mdadm --detail /dev/md2
/dev/md2:
Version : 1.2
Raid Level : raid0
Total Devices : 4
Persistence : Superblock is persistent
State : inactive
Working Devices : 4
Name : elephant:2 (local to host elephant)
UUID : bf34e086:5a85e77b:a2bbe941:b399e756
Events : 17940326
Number Major Minor RaidDevice
- 8 32 - /dev/sdc
- 8 0 - /dev/sda
- 8 48 - /dev/sdd
- 8 16 - /dev/sdb
# mdadm --examine /dev/sda (the other three drives are identical
except for UUIDs and checksums)
/dev/sda:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : bf34e086:5a85e77b:a2bbe941:b399e756
Name : elephant:2 (local to host elephant)
Creation Time : Wed Jan 30 07:38:18 2013
Raid Level : raid6
Raid Devices : 5
Avail Dev Size : 5860531120 (2794.52 GiB 3000.59 GB)
Array Size : 8790795264 (8383.56 GiB 9001.77 GB)
Used Dev Size : 5860530176 (2794.52 GiB 3000.59 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
Unused Space : before=1960 sectors, after=944 sectors
State : clean
Device UUID : 70335f31:bac3b30a:4b413322:16d0ca05
Internal Bitmap : 8 sectors from superblock
Update Time : Wed Apr 10 16:35:51 2019
Bad Block Log : 512 entries available at offset 72 sectors
Checksum : f724515a - correct
Events : 17940326
Layout : left-symmetric
Chunk Size : 512K
Device Role : Active device 1
Array State : AAAAA ('A' == active, '.' == missing, 'R' == replacing)
Relevant (lack of) dmesg output:
# dmesg|grep md
[ 2.453207] md: Waiting for all devices to be available before autodetect
[ 2.457392] md: If you don't use raid, use raid=noautodetect
[ 2.461771] md: Autodetecting RAID arrays.
[ 2.465981] md: autorun ...
[ 2.470140] md: ... autorun DONE.
[ 5840.029700] md: md2 stopped.
[ 6307.979894] md: md2 stopped.
[ 6307.981624] md: md2 stopped.
[ 6501.517031] md: md2 stopped.
[ 7028.706986] md: md2 stopped.
[ 7028.709221] md: md2 stopped.
# uname -a
Linux elephant 4.14.42-gentoo #2 SMP Mon May 21 23:25:01 UTC 2018
x86_64 Intel(R) Core(TM)2 Quad CPU Q9400 @ 2.66GHz GenuineIntel
GNU/Linux
# mdadm --version
mdadm - v4.1 - 2018-10-01
--
Mark
