mismatch_cnt != 0, member content mismatch, but md says the mirror is good

[Michael ODonnell]

I executed commands as they would have been during the cron.weekly run and
I can now see why our simple monitor script would conclude the RAID had
a problem based on the resultant contents of /proc/mdstat.  During the
"check" operation the RAID state is described as "clean, resyncing"
by mdadm and I don't know whether the RAID should be regarded as being
fault-tolerant in that state, though Mr.  Bilow indicated that it should
and I see no screaming evidence to the contrary.

Before the "check" operation:

   ### ROOT ### cbc1:~ 545---> cat /sys/block/md0/md/array_state
   clean

   ### ROOT ### cbc1:~ 546---> cat /sys/block/md0/md/sync_action
   idle

   ### ROOT ### cbc1:~ 547---> cat /proc/mdstat
   Personalities : [raid1]
   md0 : active raid1 sdb5[1] sda5[0]
         951409344 blocks [2/2] [UU]

   unused devices: <none>

Trigger the check:

   ### ROOT ### cbc1:~ 548---> echo check > /sys/block/md0/md/sync_action

After the check:

   ### ROOT ### cbc1:~ 549---> cat /sys/block/md0/md/array_state
   clean

   ### ROOT ### cbc1:~ 550---> cat /sys/block/md0/md/sync_action
   check

   ### ROOT ### cbc1:~ 551---> cat /proc/mdstat
   Personalities : [raid1]
   md0 : active raid1 sdb5[1] sda5[0]
         951409344 blocks [2/2] [UU]
         [>....................]  resync =  0.1% (958592/951409344) finish=132.1min speed=119824K/sec

   unused devices: <none>

   ### ROOT ### cbc1:~ 552---> mdadm --query --detail /dev/md0
   /dev/md0:
           Version : 0.90
     Creation Time : Fri Jan 22 11:08:38 2010
        Raid Level : raid1
        Array Size : 951409344 (907.33 GiB 974.24 GB)
     Used Dev Size : 951409344 (907.33 GiB 974.24 GB)
      Raid Devices : 2
     Total Devices : 2
   Preferred Minor : 0
       Persistence : Superblock is persistent

       Update Time : Tue Feb 23 09:42:14 2010
             State : clean, resyncing
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

    Rebuild Status : 0% complete

              UUID : daf8dd0b:00087a40:d5caa7ee:ae05b3aa
            Events : 0.56

       Number   Major   Minor   RaidDevice State
          0       8        5        0      active sync   /dev/sda5
          1       8       21        1      active sync   /dev/sdb5