#cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] [faulty]
md1 : active raid1 sda1[0]
      204736 blocks [2/1] [U_]

md2 : active raid1 sda2[2] sdb2[1]
      731342784 blocks [2/1] [_U]

unused devices: <none>

================================================================================================
 # mdadm --detail /dev/md2
/dev/md2:
        Version : 0.90
  Creation Time : Sun Dec 13 16:18:50 2009
     Raid Level : raid1
     Array Size : 731342784 (697.46 GiB 748.90 GB)
  Used Dev Size : 731342784 (697.46 GiB 748.90 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Wed Jul 20 13:31:07 2011
          State : active, degraded
 Active Devices : 1
Working Devices : 2
================================================================================================
# mdadm --examine /dev/sda2
/dev/sda2:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 43ceded2:e7e60c3b:a4d2adc2:26fd5302
  Creation Time : Sun Dec 13 16:18:50 2009
     Raid Level : raid1
  Used Dev Size : 731342784 (697.46 GiB 748.90 GB)
     Array Size : 731342784 (697.46 GiB 748.90 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2

    Update Time : Wed Jul 20 13:38:59 2011
          State : clean
 Active Devices : 1
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 1
       Checksum : 67c6b927 - correct
         Events : 18458847


      Number   Major   Minor   RaidDevice State
this     2       8        2        2      spare   /dev/sda2

   0     0       0        0        0      removed
   1     1       8       18        1      active sync   /dev/sdb2
   2     2       8        2        2      spare   /dev/sda2

================================================================================================
 # mdadm --examine /dev/sdb2
/dev/sdb2:
          Magic : a92b4efc
        Version : 0.90.00
           UUID : 43ceded2:e7e60c3b:a4d2adc2:26fd5302
  Creation Time : Sun Dec 13 16:18:50 2009
     Raid Level : raid1
  Used Dev Size : 731342784 (697.46 GiB 748.90 GB)
     Array Size : 731342784 (697.46 GiB 748.90 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 2

    Update Time : Wed Jul 20 13:39:09 2011
          State : clean
 Active Devices : 1
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 1
       Checksum : 67c6b94d - correct
         Events : 18458851


      Number   Major   Minor   RaidDevice State
this     1       8       18        1      active sync   /dev/sdb2

   0     0       0        0        0      removed
   1     1       8       18        1      active sync   /dev/sdb2
   2     2       8        2        2      spare   /dev/sda2

 Failed Devices : 0
  Spare Devices : 1

           UUID : 43ceded2:e7e60c3b:a4d2adc2:26fd5302
         Events : 0.18458666

    Number   Major   Minor   RaidDevice State
       2       8        2        0      spare rebuilding   /dev/sda2
       1       8       18        1      active sync   /dev/sdb2
================================================================================================