reiser4: data recovery after mkfs.reiser4?

reiser4: data recovery after mkfs.reiser4?

[Christian Trefzer]

Hi folks,

a buggy script I wrote dared to mkfs a reiser4 partition after failing
to properly tar up its contents - not that my life would depend on them,
but it would save me a few hours if I could get the stuff back.

Other than mkfs.reiser4, mount and unmount, nothing was done to the
device ; ) Is there any way to recover most of what was stored on the
now nuked fs?

TIA,
Chris

Re: reiser4: data recovery after mkfs.reiser4?

[Quinn Harris]

I really doubt there is any solution that would take less than a few hours.  I 
am sure it is possible to recover much of the data but to the best of my 
knowledge no tool exists that can recover from an abandoned root node (for 
reiser4).  Though I believe recovery in this case would just involve finding 
the root node (think that is reasonably tractable, but slow) fixing the 
superblock to point to that and let fsck do its thing.  

I don't think the root node has a magic number that advertises root, but 
internal nodes do have a recognizable signature and in principal one could 
deduce which is the root from a collection of the internal nodes.

Note that reiser4 packs lots of data in single nodes.  If you create a fresh 
fs with only a few small files they will reside entirely in the root node, 
which will be clobbered by a mkfs.  There is a very good change that mkfs 
will clobber a little bit of data, but less than 4K.

I am sure a few thousand dollars would buy you a solution.  Maybe less.

On Tuesday 19 December 2006 1:20 pm, Christian Trefzer wrote:
> Hi folks,
>
> a buggy script I wrote dared to mkfs a reiser4 partition after failing
> to properly tar up its contents - not that my life would depend on them,
> but it would save me a few hours if I could get the stuff back.
>
> Other than mkfs.reiser4, mount and unmount, nothing was done to the
> device ; ) Is there any way to recover most of what was stored on the
> now nuked fs?
>
> TIA,
> Chris

Re: reiser4: data recovery after mkfs.reiser4?

[Christian Trefzer]

Hi,

On Wed, Dec 20, 2006 at 03:05:33PM -0700, Quinn Harris wrote:
> I really doubt there is any solution that would take less than a few
> hours.  I am sure it is possible to recover much of the data but to
> the best of my knowledge no tool exists that can recover from an
> abandoned root node (for reiser4).  Though I believe recovery in this
> case would just involve finding the root node (think that is
> reasonably tractable, but slow) fixing the superblock to point to that
> and let fsck do its thing.  
> 
> I don't think the root node has a magic number that advertises root,
> but internal nodes do have a recognizable signature and in principal
> one could deduce which is the root from a collection of the internal
> nodes.
> 
> Note that reiser4 packs lots of data in single nodes.  If you create a
> fresh fs with only a few small files they will reside entirely in the
> root node, which will be clobbered by a mkfs.  There is a very good
> change that mkfs will clobber a little bit of data, but less than 4K.
> 
> I am sure a few thousand dollars would buy you a solution.  Maybe
> less.

Thanks for your concern!  However, with the additional flags Vladimir
mentioned, I managed to recover all but two shared library files which
could be easily copied from a working system.

I already answered Vladimir's posting twice - one "thanks, I'll try
that" and one success report.  It just so happens that a LOT of mails I
send to the list never gets through, no idea why.

Regards,
Chris

Re: reiser4: data recovery after mkfs.reiser4?

[Michael Weissenbacher]

Hi,
> I already answered Vladimir's posting twice - one "thanks, I'll try
> that" and one success report.  It just so happens that a LOT of mails I
> send to the list never gets through, no idea why.
Could someone resend that info to the list? I'm sure others would be 
interested too.

Michael

Re: reiser4: data recovery after mkfs.reiser4?

[Christian Trefzer]

On Thu, Dec 21, 2006 at 12:35:04PM +0100, Michael Weissenbacher wrote:
> Could someone resend that info to the list? I'm sure others would be
> interested too.

I just replied I'd try what Vladimir said, and so I did - successfully.
But here you go, hoping this one will come through.  I even stopped
signing my outgoing email to this list, to no avail.

For me,

	fsck.reiser4 -u -O --build-fs $device

did the trick.  The file system was killed by a scripted mkfs.reiser4
followed by a mount and unmount.  Only two files were missing
afterwards, while lost+found was globbered with the obvious heap of
previously deleted files, most of them being 0 in size.

Kind regards,
Chris