ext3 corrupted

[Madison Kelly]

John Van Ostrand wrote:
> On Sat, 2007-07-21 at 17:37 -0400, Marc Lijour wrote:
> 
>> I have a drive that got corrupted (just before it started to send SMART 
>> alerts). I can't mount it and I get this error message:
>>
>> EXT3-fs error (device sda12): ext3_check_descriptors: Block bitmap for group 
>> 896 not in group (block 16777317)!
>>
>> I can't mount it as ext2 either, and I can't mount sda either. auto as type 
>> does not work either.
>>
>> Running fsck and accepting all actions with a 'y' seems to have no effect. I 
>> can't mount the disk and when I get to do fsck again I get the same actions.
>>
>> dd works.
>>
>> Do you know a way to get the data back?
> 
> 
> First, let the drive cool down. Sometimes heat and the expansion of the
> platters can cause read errors.
> 
> Next, get another drive and perform a dd from the dying drive to the
> working drive. I would recommend booting from a rescue CD. Disc 1 from
> any Red Hat/Fedora/CentOS will act as a rescue CD by typing "linux
> rescue" at the boot prompt. Ubunutu's live boot would work as well and
> give you some GUI tools too. Use the 'noerror' option when using dd so
> that disk read errors will not abort the copy.
> 
> If the data is particularly sensitive you may want to make another copy
> before continuing.
> 
> I can't comment on the tools to use to fix that file system, fsck has
> generally worked for me. If you don't want to get your hands dirty there
> are labs that will restore the data for you by working a little harder
> to correct the file system errors.
> 
> Good luck.

These are good suggestions, specially the 'dd' one.

One trouble with any journaled file system is that data recovery is very 
difficult. An ext2 partition is simple to recover, by comparison. It's 
to the point now where if I have an ext3 (or other journaled) FS, I get 
paranoid about backups. My personal view/experience is that it's just 
not possible, but I am also not an expert.

I would suggest that, if your data is critical, do not attempt anything 
beyond the 'dd' yourself.

Ontrack (http://www.ontrackdatarecovery.com/ontrack) was the DR house 
I've used in the past. They're very talented, and recovered a physically 
defective drive a client had (whose tape backup had silently failed, 
ending my trust of tape backups ever since). I believe it was about 
$1,700 and they were unable to recover the directory structure, but all 
the data was there. It took about two more days to recreate the 
directory structure, but in the end we got all the data back. I believe 
they will look at your drive and give you an idea of the likely hood of 
recovering your data before doing billable work. At least they did back 
when I last needed them.

I would *only* suggest trying anything further on your defective disk if 
you get a quote from them (or another DR house) and you decide it's too 
expensive (ie: 'nothing to lose'). If you do manage to make a dd image, 
try doing data recovery on a copy of the image. You really do not want 
to touch the source drive *any* more than you have to.

I wish I had better news. :( Journaling is a double-edged sword.

Madi
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