Buffalo LS-Q4.0 Raid 5 XFS errors

[Dave Chinner]

On Thu, Mar 29, 2012 at 06:29:14PM -0500, Kirk Anderson wrote:
> These two matched.
> 
> root at LS-QLF55:~# dd if=/dev/sda6 bs=512 count=1 2> /dev/null | hexdump -C >
> dump_sda6.txt
> root at LS-QLF55:~# dd if=/dev/md2 bs=512 count=1 2> /dev/null | hexdump -C >
> dump_md2.txt
> root at LS-QLF55:~# diff dump_sda6.txt dump_md2.txt
> root at LS-QLF55:~#
> 
> root at LS-QLF55:~# dd if=/dev/md2 bs=512 count=4 2> /dev/null | hexdump -C
> 00000000  58 46 53 42 00 00 10 00  00 00 00 00 2b 4e 92 c0
> |XFSB........+N..|
> 00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
> |................|
> 00000020  1b 5a c5 ad cc e3 40 11  87 4d f5 8e 9b f8 37 c0
> |.Z.... at ..M....7.|
> 00000030  00 00 00 00 20 00 00 07  00 00 00 00 00 00 01 00  |....
> ...........|
> 00000040  00 00 00 00 00 00 01 01  00 00 00 00 00 00 01 02
> |................|
> 00000050  00 00 00 30 01 5a 74 a0  00 00 00 20 00 00 00 00  |...0.Zt....
> ....|
> 00000060  00 00 80 00 3d 84 10 00  01 00 00 10 00 00 00 00
> |....=...........|
> 00000070  00 00 00 00 00 00 00 00  0c 0c 08 04 19 00 00 19
> |................|
> 00000080  00 00 00 00 00 04 50 c0  00 00 00 00 00 00 02 ce
> |......P.........|
> 00000090  00 00 00 00 0b ba 45 ab  00 00 00 00 00 00 00 00
> |......E.........|
> 000000a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
> |................|
> 000000b0  00 00 00 00 00 00 00 02  00 00 00 10 00 00 00 30
> |...............0|
> 000000c0  00 0c 10 00 00 00 10 00  00 00 00 00 00 00 00 00
> |................|
> 000000d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
> |................|
> *
> 00000800

The AGF, AGI and AGFL have all been zeroed. Something has
overwritten them. Your filesysetm is likely to be toast.

> 
> 
> root at LS-QLF55:~# xfs_db -c "sb 0" -c p -c "agf 0" -c p -c "agi 0" -c p
> /dev/md2
> cache_node_purge: refcount was 1, not zero (node=0xb1698)
> xfs_db: cannot read root inode (22)

And that means the zeroing has extended well into the filesystem,
and your root directory has been lost. There's really not that much
that reapir can do for you at this point execpt make a mess. There
is no AGI left to find where in-use inodes might live to recover
them, and the directory structure cannot be used to find them,
either, so I think the only thing you can do now is start on
disaster recovery.

Christoph had a patch to xfs_repair that allowed it to run
xfs_irecover like functionality - I don't think he ever posted it,
so you might just have to find the original xfs_irecover utility and
make use of that to extract whatever you can from the busted
filesystem.

Other than that, I think that there's little we can do to help you
recover the filesystem intact at this point....

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com