Disk inconsistency

Sandy Rutherford sandy at krvarr.bc.ca
Wed Sep 28 04:08:18 PDT 2005

>>>>> On Wed, 28 Sep 2005 06:25:44 -0400, 
>>>>> Michael Conlen <m at obmail.net> said:

 > I have reason to believe that a set of mirrored disks became  
 > inconsistent recently. Since reviving the disk array the system it's  
 > attached to has become highly unstable. It appears to deadlock every  
 > few hours. No errors, no logs, no response to keyboard, ping or other  
 > network requests.

 > Each reboot takes several passes with FSCK to get the disks in to a  
 > clean state to boot with again.

 > Can anyone confirm that reading data from a set of mirrored drives  
 > which are inconsistent would cause this type of symptom?

A month ago I had one drive in a raid 1 volume "intermittently fail".
I started seeing occasional (as in only once or twice per week) read
errors in the logs for the volume in question; however, the drive
didn't fail catastrophically enough for me to identify which one of
the 2 drives was bad.  After this happened a few times, I started
seeing exactly the behaviour that you described above.  At the time, I
conjectured that the mirrored disks had become inconsistent.
Fortunately, I was able to identify the bad drive soon after. 
After replacing the drive and rebuilding the redundant data, the
system has been perfectly stable.

Based on my experience, I would guess that it is indeed possible that
your raid 1 data is inconsistent.  The difficulty is determining which
of the 2 disks has good data (if either).  If you have a third drive
of the same model, you might try replacing in succession each of the
two drives with the third and rebuilding the reduntand data.  It goes
without saying that backing up to tape would be a good idea before
mucking about with the drives.  If your system isn't stable enough to
dump the raid volume to tape, try offlining one or the other of the
drives to see if that helps.

You didn't state your raid setup (hardware or software?).  In my case,
I am using hardware raid (a Mylex extremeRAID 1100 controller) with
SCSI disks.


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