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

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