[Btrfs-devel] reversing the effects of mkfs.btrfs?

[Chris Mason]

On Sunday 27 April 2008, Peter Teoh wrote:
> Ok, I have done some experiments:
> :-( :-( :-( :-( :-( :-( :-( :-( :-( :-( :-( :-( :-( :-( :-( :-(
>
> This is no good.
>
> I did some test on a 100M partition.
>
> 1.   create/mount a ext3 fs.
> 2.   create 50 identical files (with random contents inside).
> 3.   dismount it.
> 4.   do a dd backup of the image.
> 5.   execute mkfs.btrfs on it.
> 6.   do a dd backup of the image.
> 7.   compare incrementally the hexadecimal output of the two dd image
> above.
>
> The results?   Disaster, lots of binary diff.   Starting with 0x400 offset:

mkfs.btrfs zeros the first and last 2MB of the drive.  As a percentage of the 
40GB, this is pretty small.


>
> Doing a mkfs.ext3 after the mkfs.btrs does not restore back any
> information, if not destroying even more information.

mkfs won't restore information, it is meant to initialize things and remove 
markers from other filesystems.  But, 99% of the data is still going to be 
there.

A quick search found:

http://www.recoveryourdata.com/linux-data-recovery.html

People on the ext3 development lists might have other suggestions.

-chris