[Tfug] Drive recovery

[Harry McGregor]

Hi John

John Gruenenfelder wrote:
> I've recently had a drive at work begin the throes of death.  While SMART did
> not warn me about any problems beforehand, it did tell me later that the drive
> had run out of spare sectors.  Some random sector went bad, but the drive no
> longer has any spare sectors left in its pool to remap the bad one.
>
> This means that any attempt to read data from that sector results in a low
> level read error from the drive.
>
> To make matters worse, whatever sector (or sectors) ate it, there was
> important XFS filesystem metadata there because I can no longer mount the
> filesystem at all.  Bah!
>
> Now, it seems like the immediate problem is that as soon as any program gets a
> low level read error, it promptly aborts.  If I could force mount, xfs_check,
> xfs_repair, or some other program to keep trying, maybe it could work?  I know
> ext2/3 keeps superblock backups for emergencies.  I'm hoping that whatever XFS
> data got clobbered is residing elsewhere on the drive.  But since every
> program aborts right away, they never get a chance to try fallback methods (if
> any exist).
>
> This particular partition was a very large data partition.  The rest of the
> system is backed up frequently, but the data drives are too large.  Therefore,
> it is the users' responsibility to backup important data on their own or
> direct the machine's backup system as to what is important.  But... very few
> users ever bother to do this, so I need to try my best to get any data off the
> drive.
>
> So, any ideas on how I might mount it?  That would be easiest.  Alternatively,
> I'll need some sort of lower-level tool to scan the drive for lost
> contents... perhaps something that scans for known file types maybe?  I'm not
> really sure what's available.  I did find recoverdm in the Debian repository,
> but it looks to be focused on trying bad sectors on CD/DVD media and less so
> on hard drives.  Another possible solution would be to copy the whole
> partition into an image file and have tools work on it that way since they
> would no longer have to deal with read errors.  Unfortunately, the partition
> which failed was the largest one and there is currently insufficient space in
> the machine to hold a copy of that partition.
>
> I'm open to any suggestions on how to get some data off this partition.  Just,
> presumably, one bad sector can't be that hard to work around, right?  :(
>
>   
My first suggestion would be a dd_rescue to a file on a "new" drive, and
attempting file system repair on the loop file instead of on the
"failing" drive.

How big is it?  I might have enough capacity in spare drives laying
around depending on the size.


                                     Harry