Re: Unable to mount degraded RAID5

[Chris Murphy <lists@colorremedies.com>]

On Mon, Jul 4, 2016 at 1:11 PM, Tomáš Hrdina <thomas.rkh@gmail.com> wrote:
> Result from dmesg:
> http://sebsauvage.net/paste/?4e8e95b5eafbf675#ybToBzZ/WAoRjjugeH6N2YXZKEBlswaNI/J41GBmFYU=

[10849.041749] BTRFS info (device sda): allowing degraded mounts
[10849.041754] BTRFS info (device sda): disk space caching is enabled
[10849.041756] BTRFS: has skinny extents
[10849.090553] BTRFS error (device sda): bad tree block start
10160120763642806272 12678831570944
[10849.090676] BTRFS error (device sda): bad tree block start
10160120763642806272 12678831570944
[10849.090700] BTRFS: failed to read chunk tree on sda
[10849.100153] BTRFS: open_ctree failed


Try 'mount -o ro,degraded,recovery


>
> sudo btrfs check /dev/sda
> warning, device 3 is missing
> checksum verify failed on 12678831570944 found 3DC57E3E wanted 771D2379
> checksum verify failed on 12678831570944 found 3DC57E3E wanted 771D2379
> bytenr mismatch, want=12678831570944, have=10160133442474442752
> Couldn't read chunk tree
> Couldn't open file system

Want and have are way far apart. If the mount command above still
fails then I'd like to see:

# btrfs-show-super -fa /dev/sda
# btrfs-show-super -fa /dev/sdb

Pretty much look for any discrepancies in generation, root and
chunk_root addresses, both in the main part of the super as well as in
the backups.

# btrfs-find-root /dev/sda

Maybe it's possible to use a different tree to get it mounted. I don't
know what happened but merely a failing device should not either break
checksums or lose the ability to mount the proper tree; but for sure
one of the backups should work.

Have you done a scrub on this file system and do you know if anything
was fixed or if it always found no problem?



-- 
Chris Murphy