Hi Neil,
It can happen that a spare has a higher event count than a in-array drive.
For exampe: RAID1 with two drives is rebuilding one of the drives.
Then the "good" drive fails. As a result, MD stops the rebuild and
ejects the rebuilding drive from the array. The failed drive stays in
the array, because RAID1 never ejects the last drive. However, the
"good" drive fails all IOs, so the ejected drive has a larger event
count now.
Now if MD is stopped and re-assembled, mdadm considers the spare drive
as the chosen one:
root@vc:/mnt/work/alex/mdadm-neil# ./mdadm --assemble /dev/md200
--name=alex --config=none --homehost=vc --run --auto=md --metadata=1.2
--verbose --verbose /dev/sdc2 /dev/sdd2
mdadm: looking for devices for /dev/md200
mdadm: /dev/sdc2 is identified as a member of /dev/md200, slot 0.
mdadm: /dev/sdd2 is identified as a member of /dev/md200, slot -1.
mdadm: added /dev/sdc2 to /dev/md200 as 0 (possibly out of date)
mdadm: no uptodate device for slot 2 of /dev/md200
mdadm: added /dev/sdd2 to /dev/md200 as -1
mdadm: failed to RUN_ARRAY /dev/md200: Input/output error
mdadm: Not enough devices to start the array.
Kernel doesn't accept the non-spare drive considering it as non-fresh:
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.679396] md: md200 stopped.
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.686870] md: bind<sdc2>
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687623] md: bind<sdd2>
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687675] md: kicking
non-fresh sdc2 from array!
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687680] md: unbind<sdc2>
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.687683] md: export_rdev(sdc2)
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.693574]
md/raid1:md200: active with 0 out of 2 mirrors
May 27 12:42:28 vsa-00000505-vc-0 kernel: [343203.693583] md200:
failed to create bitmap (-5)
This happens with the latest mdadm from git, and kernel 3.8.2.
Is this the expected behavior?
Maybe mdadm should not consider spares at all for its "chosen_drive"
logic, and perhaps not try to add them to the kernel?
Superblocks of both drives:
sdc2 - the "good" drive:
/dev/sdc2:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : 8e051cc5:c536d16e:72b413fa:e7049d4b
Name : zadara_vc:alex
Creation Time : Mon May 27 11:33:50 2013
Raid Level : raid1
Raid Devices : 2
Avail Dev Size : 975063127 (464.95 GiB 499.23 GB)
Array Size : 209715200 (200.00 GiB 214.75 GB)
Used Dev Size : 419430400 (200.00 GiB 214.75 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
Unused Space : before=1968 sectors, after=555632727 sectors
State : clean
Device UUID : 1f661ca3:fdc8b887:8d3638ab:f2cc0a40
Internal Bitmap : 8 sectors from superblock
Update Time : Mon May 27 11:34:57 2013
Checksum : 72a97357 - correct
Events : 9
sdd2 - the "rebuilding" drive:
/dev/sdd2:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : 8e051cc5:c536d16e:72b413fa:e7049d4b
Name : zadara_vc:alex
Creation Time : Mon May 27 11:33:50 2013
Raid Level : raid1
Raid Devices : 2
Avail Dev Size : 976123417 (465.45 GiB 499.78 GB)
Array Size : 209715200 (200.00 GiB 214.75 GB)
Used Dev Size : 419430400 (200.00 GiB 214.75 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
Unused Space : before=1968 sectors, after=556693017 sectors
State : clean
Device UUID : 9abc7fa9:6bf95a51:51f2cd65:14232e81
Internal Bitmap : 8 sectors from superblock
Update Time : Mon May 27 11:35:56 2013
Checksum : 3e793a34 - correct
Events : 26
Device Role : spare
Array State : A. ('A' == active, '.' == missing, 'R' == replacing)
Thanks,
Alex.
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