ext3 corrupted

[Jamon Camisso]

Marc Lijour wrote:
>> 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.
> 
> Thank you for all these great tips. It's hard to keep up with the mail
> with one less computer ;)
> 
> I have 2 disks. My data is one the drive which failed. I commented it out
> from /etc/fstab and I stopped using it. Now the second drive seems to be
> failing. I even got the BIOS not founding the drives at boot time once.
> Which makes me wonder if the problem does not come from the board.
> 
> In any case, I have a technical question about dd. My data is on
> /dev/sda10 (around 100GB). Say I plug another SATA drive (say a new 500GB
> drive). How should I proceed? I assume I should first create a partition
> with exactly the same size (or a little more) on the new drive, and then
> run dd. Is that correct? At that point, you'll understand I take no chance
> with my data ;)

Try mounting the dd image with mount -o loop. You can then copy the data 
from the mounted image, not the image itself, onto whatever size 
partition you choose on the 500gb drive.

Jamon
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