Physical disk (/dev/hda2) is "removed" from mdadm raid array(/dev/md2) after a reboot

Issue

• After a reboot, the /dev/hda2 disk was gone from the mdadm array /dev/md2 :

# mdadm --detail /dev/md2
/dev/md2:
        Version : 00.90.01
  Creation Time : Sat Sep 16 11:45:26 2006
     Raid Level : raid1
     Array Size : 5172864 (4.93 GiB 5.30 GB)
    Device Size : 5172864 (4.93 GiB 5.30 GB)
   Raid Devices : 2
  Total Devices : 1
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Thu Dec 16 05:57:21 2010
          State : clean, degraded
 Active Devices : 1
Working Devices : 1
 Failed Devices : 0
  Spare Devices : 0

           UUID : 2693ade7:d6ab52a5:52bd9e0c:9ce447e7
         Events : 0.39983614

    Number   Major   Minor   RaidDevice State
       0       0        0        -      removed
       1      22        2        1      active sync   /dev/hdc2
#

• The logs contained the following:

# egrep -i 'md2|hda2' /var/log/message*
/var/log/messages:Dec 12 11:33:10 <hostname> kernel:  hda: hda1 hda2 hda3 hda4 < hda5 hda6 hda7 >
/var/log/messages:Dec 12 11:33:10 <hostname> kernel: md: hda2 has different UUID to hdc7
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: hda2 has different UUID to hdc6
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: hda2 has different UUID to hdc5
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: hda2 has different UUID to hdc3
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md:  adding hda2 ...
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: created md2
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: bind<hda2>
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: running: <hdc2><hda2>
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: kicking non-fresh hda2 from array!
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: unbind<hda2>
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: export_rdev(hda2)
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: raid1: raid set md2 active with 1 out of 2 mirrors
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: considering hda2 ...
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md:  adding hda2 ...
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: md2 already running, cannot run hda2
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: export_rdev(hda2)
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: considering hda2 ...
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md:  adding hda2 ...
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: md2 already running, cannot run hda2
/var/log/messages:Dec 12 11:33:11 <hostname> kernel: md: export_rdev(hda2)
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: considering hda2 ...
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md:  adding hda2 ...
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: md2 already running, cannot run hda2
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: export_rdev(hda2)
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: considering hda2 ...
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md:  adding hda2 ...
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: md2 already running, cannot run hda2
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: export_rdev(hda2)
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: considering hda2 ...
/var/log/messages:Dec 12 11:32:26 <hostname> fsck: /dev/md2: clean, 2222/647680 files, 290857/1293216 blocks
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md:  adding hda2 ...
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: md2 already running, cannot run hda2
/var/log/messages:Dec 12 11:33:12 <hostname> kernel: md: export_rdev(hda2)
/var/log/messages:Dec 12 11:33:13 <hostname> kernel: md: considering hda2 ...
/var/log/messages:Dec 12 11:33:13 <hostname> kernel: md:  adding hda2 ...
/var/log/messages:Dec 12 11:33:13 <hostname> kernel: md: md2 already running, cannot run hda2
/var/log/messages:Dec 12 11:33:13 <hostname> kernel: md: export_rdev(hda2)
/var/log/messages:Dec 12 11:33:13 <hostname> kernel: EXT3 FS on md2, internal journal