Re: Btrfs Array Recovery

[Stefan Behrens <sbehrens@giantdisaster.de>]

On 4/12/2012 11:25 PM, Travis Shivers wrote:
> A few months ago, my btrfs storage array became corrupted because of a
> power failure. A while ago, I made this thread to try and resolve the
> problem. (http://www.digipedia.pl/usenet/thread/11904/15955/) You can
> find detailed information about the problem in the previous thread,
> but I am happy to provide any other details. It didn't really go
> anywhere in the way of solving my problem. The thread ended in me
> waiting for a patch that would allow me to mount my corrupted array
> which was around 2 months ago.

You were running 3.2.8, that shouldn't corrupt filesystems anymore on
power failure. This is unexpected.

> 
> While I have been waiting, I have tried several things. One of the
> things that I tried was installing the latest Linux kernel (3.4 RC1)
> with the btrfs integrity checking enabled. I read about this module
> here: (http://lwn.net/Articles/466493/) With the option compiled in, I
> have had severe mounting problems. I can only try to mount the array
> once before it does some strange things. The first time I try and
> mount it, it fails, but logs this in dmesg:
> (http://pastebin.com/YwAsdjhs) It looks like there is a bug in this
> integrity checking code. After I try to mount the drive after the
> first time, it just hangs and doesn't return anything or log anything
> in dmesg. Even trying to mount the drive without the integrity
> checking problem hangs and has the same problems.

[   43.809870] parent transid verify failed on 5568194412544 wanted
43477 found 43151
[   43.809875] failed mirror was 0
[   43.826531] ------------[ cut here ]------------
[   43.826573] kernel BUG at fs/btrfs/extent_io.c:1890!

This is not related to the integrity check code.

The same issue is reported in the thread "Re: kernel BUG at
fs/btrfs/extent_io.c:1890!". You might want to monitor that thread to
get the fix for it as early as possible.

> 
> I have also grabbed the latest version of btrfs-progs since I saw that
> btrfsck could now repair some corruptions. I built the utilities and
> executed btrfsck. This is the result of the command:
> (http://pastebin.com/CEyvy17r) I saw that there was an error occurring
> in the code at line 1864, so I commented out that line which had the
> text: BUG_ON(rec->is_root);
> I then recompiled the utilities and executed btrfsck again and got
> this: (http://pastebin.com/ihYmuCAm) I also tried btrfsck with the
> repair option with these results: (http://pastebin.com/gnrStyqh)
> 
> Another thing that I have experimented with is btrfs-restore. I have
> been somewhat successful in using this tool to restore the files. The
> main problem that I have is that it cannot restore over half of the
> files on the array and just puts an empty file with a size of 0. It
> does restore the other half of the array perfectly. On the files that
> it cannot restore, it returns a return code of -3. For example, here
> is an example of a file which is unable to be restored by this tool:
> (http://pastebin.com/Rg5a0xdG) I read more about this tool here
> (http://btrfs.ipv5.de/index.php?title=Restore) I tried this tool with
> '-u 1' and '-u 2' flags, which did not help anything. I do not think
> that half of my array is corrupted since it was just a power failure
> and the drive is also mirrored, which should provide some redundancy.

And btrfsck is not 100% finished yet, as far as I understood it. There
is always room for improvement. To wait some more time might be a good idea.