Hello,
On Ubuntu 12.04 with a standard kernel (3.2) we've been seeing very
strange behavior with our RAID1 sets, both with superblock 1.2, and with
0.9. The system has been instructed to come up with a degraded array in
initrd, in case this is relevant. Here is an example of what is
happening. We have 5 RAID1 sets on a server. They live on partitions on
/dev/sda and /dev/sdb. The sever comes up with 2 out of 5 sets degraded,
and the others just fine.
Trying to re-add or add the partitions into the arrays fails like this:
# mdadm /dev/md2 --re-add /dev/sda6
mdadm: --re-add for /dev/sda6 to /dev/md2 is not possible
# mdadm /dev/md2 --add /dev/sda6
mdadm: /dev/sda6 reports being an active member for /dev/md2, but a
--re-add fails.
mdadm: not performing --add as that would convert /dev/sda6 in to a spare.
mdadm: To make this a spare, use "mdadm --zero-superblock /dev/sda6" first.
Here is some more information from /proc/mdstat, dmesg, and syslog.
# cat /proc/mdstat
md2 : active raid1 sdb6[1]
20479872 blocks [2/1] [_U]
md3 : active raid1 sdb7[0]
10239872 blocks [2/1] [U_]
# dmesg | grep md2
[ 4.087037] md/raid1:md2: active with 1 out of 2 mirrors
[ 4.087147] md2: detected capacity change from 0 to 20971388928
[ 4.119168] md2: unknown partition table
[ 12.383035] EXT4-fs (md2): mounted filesystem with ordered data mode.
Opts: (null)
# dmesg | grep md3
[ 4.083084] md/raid1:md3: active with 1 out of 2 mirrors
[ 4.083230] md3: detected capacity change from 0 to 10485628928
[ 4.180986] md3: unknown partition table
[ 9.631814] EXT4-fs (md3): mounted filesystem with ordered data mode.
Opts: (null)
# ls -l /dev/sda6
brw-rw---- 1 root disk 8, 6 Jun 12 16:54 /dev/sda6
# ls -l /dev/sda7
brw-rw---- 1 root disk 8, 7 Jun 12 16:54 /dev/sda7
# grep md2 /var/log/syslog
Jun 12 16:54:32 ps2 kernel: [ 4.087037] md/raid1:md2: active with 1
out of 2 mirrors
Jun 12 16:54:32 ps2 kernel: [ 4.087147] md2: detected capacity change
from 0 to 20971388928
Jun 12 16:54:32 ps2 kernel: [ 4.119168] md2: unknown partition table
Jun 12 16:54:32 ps2 kernel: [ 12.383035] EXT4-fs (md2): mounted
filesystem with ordered data mode. Opts: (null)
Jun 12 16:54:38 ps2 mdadm[1181]: DegradedArray event detected on md
device /dev/md2
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