Re: Re-map disk sectors in userspace when rewriting after read errors

Thank you for the insight, Robin.

I already have used dd_rescue to find which sectors are bad, so I
guess I could either wait for Matthias to finish his modifications to
mdadm, or I can reconstruct the bad sectors manually (read same sector
from other disks, xor all, write to damaged disk's clone).

Weird thing though, is that when I re-read some of the bad sectors, I
didn't get I/O errors ... it's confusing!

Also, I'd rather avoid a fsck when I have bad sectors to not lose
files. I'll run fsck once I've fixed the bad sectors and resynced the
array.

On Fri, Sep 18, 2009 at 11:28 AM, Robin Hill [off-list ref] wrote:

All the 'check' action does is validate that the checksum matches the
data.  By doing this, it will also be doing a full read check on the
array (though I'm not certain what action is taken on read failures).
The 'repair' action will also rewrite any checksums which don't match
the data.

All of this requires a non-degraded array, so I suspect the 'check' and
'repair' actions will get ignored altogether on a degraded array (and
certainly won't actually work).  As the array is degraded, you _can't_
have any RAID inconsistencies.  You may have some filesystem
inconsistencies (a fsck is definitely recommended) and/or data
inconsistencies (unless you have checksums or backups to compare against
then you're stuck on finding these though).

Cheers,
   Robin
--
    ___
   ( ' }     |       Robin Hill        [off-list ref] |
  / / )      | Little Jim says ....                            |
 // !!       |      "He fallen in de water !!"                 |

-- 
       Majed B.
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html