Several unhappy btrfs's after RAID meltdown

["Ryan C. Underwood" <nemesis-lists@icequake.net>]

Hi,

I had a RAID5 double disk failure (40 megs or so bad sectors near
middle of the second failed disk), bad news but I recovered what I was
able to.

The RAID contained a dm-crypt physical volume which then contained
four logical volumes.  Two are EXT4 and two BTRFS, about 1TB in size
each.

The failure occurred while the volumes were online and in use, so in
addition to what was unreadable, all pending writes to the device
between the failure and when the problem was discovered were lost as
well.

The two ext4, fortunately, had some relatively minor corruption which
was cleared up with a few rounds of fsck.  The two btrfs are
completely unhappy though and I do not know how to proceed, since
btrfs problems are new to me.  Any suggestions are welcome.

Here is the basic picture of what is going on.

# cat /etc/fstab
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
#/dev/mapper/tr5ut-media        /mnt/media      btrfs
defaults,compress=lzo,space_cache 0       2

/dev/mapper/tr5ut-media /mnt/media      ext4 defaults 0 2

/dev/mapper/tr5ut-vicep--library        /vicepa auto
defaults,compress=lzo,space_cache  0       2

/dev/mapper/tr5ut-vicep--clones         /vicepb auto
defaults,compress=lzo,space_cache  0       2


You can see that btrfs device scan does not find anything, while
btrfs-show finds one of the volumes and not the other.  Fscking the
found volume halts due to checksum and assertion errors, while fscking
the other volume fails completely, I guess due to a missing
'superblock' type structure?


seraph:~# btrfs device scan
Scanning for Btrfs filesystems
failed to read /dev/sr0


seraph:~# btrfs-show
**
** WARNING: this program is considered deprecated
** Please consider to switch to the btrfs utility
**
failed to read /dev/sr0: No medium found
Label: vicep-library  uuid: 89b14d35-b31a-4fbe-a2d9-cb83cbcd3851
        Total devices 1 FS bytes used 254.35GB
        devid    1 size 1.00TB used 299.04GB path /dev/dm-32

Btrfs Btrfs v0.19


seraph:~# btrfsck /dev/mapper/tr5ut-vicep--library
checksum verify failed on 317874630656 wanted 8E19212D found FFFFFFA6
checksum verify failed on 317874630656 wanted 8E19212D found FFFFFFA6
checksum verify failed on 317874630656 wanted 491D9C1A found FFFFFFA6
checksum verify failed on 317874630656 wanted 8E19212D found FFFFFFA6
Csum didn't match
btrfsck: root-tree.c:46: btrfs_find_last_root: Assertion
`!(path->slots[0] == 0)' failed.
Aborted


seraph:~# btrfsck /dev/mapper/tr5ut-vicep--clones
No valid Btrfs found on /dev/mapper/tr5ut-vicep--clones


seraph:~# dpkg -l btrfs-tools
Desired=Unknown/Install/Remove/Purge/Hold
|
Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                          Version
Description
+++-=============================================-=============================================-==========================================================================================================
ii  btrfs-tools                                   0.19+20111105-2
Checksumming Copy on Write Filesystem utilities


-- 
Ryan C. Underwood, <nemesis@icequake.net>