Re: Help repairing a partition

[Chris Murphy <lists@colorremedies.com>]

On Thu, Oct 20, 2016 at 3:20 PM, Suvayu Ali <fatkasuvayu+linux@gmail.com> wrote:
> Hi,
>
> (please CC me in replies, I'm not subscribed)
>
> I'm using kernel 4.7.7-100.fc23 with btrfs-progs v4.7.1.
>
> I had my /home, /var, and /opt as subvolumes in a btrfs partition.
> Last night btrfs failed, and I was unable to mount it normally
> (leading to boot failures).  The journal had messages like this:
>
>   BTRFS: open_ctree failed
>   BTRFS error: super_total_bytes ... mismatch with fs_devices total_rw_bytes
>   BTRFS error: failed to read chunk tree: -22
>
> Finally I managed to mount it manually like this (after making a dd
> image of the partition):
>
>   # mount -t btrfs -o ro,recovery,nospace_cache /dev/sdb2 /mnt
>
> and managed to recover my data. Initially "btrfs check" yielded a few
>
>   parent transid verify failed on 101679726592 wanted 822619 found 822617
>
> and
>
>   checksum verify failed on 101756387328 found 78C8A0BC wanted B7C59D79
>
> however after backing up my data, I mounted without the "-o ro" (I got
> a transid related message, but it did mount).  "btrfs check" now spits
> out a whole bunch of:
>
>   Incorrect local backref count on 202118008832 root 259 owner 178928
> offset 41181184 found 2 wanted 7 back 0x55713fbbf150
>   Incorrect global backref count on 202118008832 found 2 wanted 7
>   backpointer mismatch on [202118008832 376832]


This is a known problem with btrfs-progs 4.7.1 it should not be used.
https://btrfs.wiki.kernel.org/index.php/Changelog#btrfs-progs_4.7.1_.28Aug_2016.29

Upgrade to 4.7.3 or 4.8.1 is advised.




>
> followed by this summary:
>
> checking csums
> checking root refs
> checking quota groups
> Counts for qgroup id: 0/257 are different
> our:            referenced 7746465792 referenced compressed 7746465792
> disk:           referenced 7746461696 referenced compressed 7746461696
> diff:           referenced 4096 referenced compressed 4096
> our:            exclusive 7746465792 exclusive compressed 7746465792
> disk:           exclusive 7746461696 exclusive compressed 7746461696
> diff:           exclusive 4096 exclusive compressed 4096
> Counts for qgroup id: 0/259 are different
> our:            referenced 135641784320 referenced compressed 135641784320
> disk:           referenced 135633862656 referenced compressed 135633862656
> diff:           referenced 7921664 referenced compressed 7921664
> our:            exclusive 135641784320 exclusive compressed 135641784320
> disk:           exclusive 135633862656 exclusive compressed 135633862656
> diff:           exclusive 7921664 exclusive compressed 7921664
> found 167864082432 bytes used err is 0
> total csum bytes: 161187492
> total tree bytes: 2021015552
> total fs tree bytes: 1725759488
> total extent tree bytes: 86228992
> btree space waste bytes: 386160897
> file data blocks allocated: 1269363683328
>  referenced 164438126592
>
> How do I repair this?

Yeah good question. I can't tell from the message whether different
counts is a bad thing, or if it's just a notification, or what. Yet
again btrfs-progs does not help the user make informed decisions, it's
really frustrating. I think that part can be ignored though for now,
and see if btrfs check --repair can fix the problem now that you have
a backup.


-- 
Chris Murphy