Did you mean
	echo repair > /sys/block/md0/md/sync_action

I run 'check' regularly and I am rather sure that it reports but does not fix the mismatches.

Here is my log of recent weekly 'check' runs. BTW, the mismatches are a mystery to me as
there was not one i/o error and no other event (the machine was not even powered down/up).
I will see how it does when the array moves (soon) to a new mobo.

Sat Oct 25 10:47:16 EST 2008 mdcheck: end mismatch_cnt=0
Sat Nov  1 14:49:11 EST 2008 mdcheck: end mismatch_cnt=0
Sat Nov  8 14:48:15 EST 2008 mdcheck: end mismatch_cnt=0
Sat Nov 15 14:49:13 EST 2008 mdcheck: end mismatch_cnt=0
Sat Nov 22 14:48:12 EST 2008 mdcheck: end mismatch_cnt=0
Sat Nov 29 14:48:10 EST 2008 mdcheck: end mismatch_cnt=16
Sat Dec  6 14:48:11 EST 2008 mdcheck: end mismatch_cnt=136
Sat Dec 13 14:48:10 EST 2008 mdcheck: end mismatch_cnt=184
Sat Dec 20 14:48:10 EST 2008 mdcheck: end mismatch_cnt=280
Sat Dec 27 14:48:07 EST 2008 mdcheck: end mismatch_cnt=288
Sat Jan  3 14:48:09 EST 2009 mdcheck: end mismatch_cnt=288
Sat Jan 10 14:48:09 EST 2009 mdcheck: end mismatch_cnt=328
Sat Jan 17 10:21:16 EST 2009 mdcheck: end mismatch_cnt=328
Sat Jan 24 10:17:13 EST 2009 mdcheck: end mismatch_cnt=400
Sat Jan 31 10:17:14 EST 2009 mdcheck: end mismatch_cnt=408
Mon Feb  2 17:23:14 EST 2009 mdcheck: end mismatch_cnt=408
Sat Feb  7 10:12:09 EST 2009 mdcheck: end mismatch_cnt=0 <<< after repair done manually

Eyal

NeilBrown wrote:

On Tue, February 24, 2009 6:40 am, Piergiorgio Sartor wrote:

quoted

Hi all,

I've a strange issue.

I've a PC with 2 HDs in RAID-10 f2 with bitmap.
There are actually 3 md devices, boot, swap and root.

It happens that one SATA cable is/was flaky, so sometimes,
at boot, /dev/sdb does not show up.
The RAID starts in degraded mode, tracking the writes
in the bitmap.
On the next reboot, /dev/sdb is again there, so it is
possible to re-add it.
The md device resyncs what is to be resynced, very
quickly, due to the bitmap.

Later, if I run a check, usually a lot of mismatches
show up.

What exactly do you mean by "check".

If you mean "look in /sys/block/md0/md/mismatch_cnt", then that is
exactly what I would expect.  The resync found some differences, just
as you would expect it to, and reported them.

However if by "check" you mean:
  echo check > /sys/block/md0/md/sync_action
  mdadm --wait /dev/md0
  cat /sys/block/md0/md/mismatch_cnt

then I would not expect any mismatches, and the resync should have
fixed them.

If it is the later, that is a real concern and I will need to look into it.
Please let me know exactly which kernel version and mdadm version you
are running.

Thanks,
NeilBrown

-- 
Eyal Lebedinsky	(eyal@eyal.emu.id.au)