Re: Fwd: Unmountable fs after power outage

[Hugo Mills <hugo@carfax.org.uk>]

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On Fri, Jan 22, 2016 at 04:11:53PM +0100, Radek Sprta wrote:
> Hello everybody,
> 
> after a recent power outage attempting to mount a my btrfs partition
> fails with the following error:
> 
> mount: wrong fs type, bad option, bad superblock on /dev/sda8,
>        missing codepage or helper program, or other error
> 
> This is what dmesg shows:
> [ 1035.236081] BTRFS (device sda8): parent transid verify failed on
> 410124288 wanted 85753 found 85755
> [ 1035.240756] BTRFS (device sda8): parent transid verify failed on
> 410124288 wanted 85753 found 85755
> [ 1035.240780] BTRFS: failed to read tree root on sda8
> [ 1035.252025] BTRFS: open_ctree failed

   Try mounting with -orecovery. That's the main approach for dealing
with transid failures.

> Below is the result of btrfs check:
> Checking filesystem on /dev/sda8
> UUID: b0486700-ff9f-4979-8735-257ff1428a0d
> checking extents
> checking free space cache
> checking fs roots
> checking csums
> checking root refs
> found 311702978854 bytes used err is 0
> total csum bytes: 271057636
> total tree bytes: 1859862528
> total fs tree bytes: 1473953792
> total extent tree bytes: 72876032
> btree space waste bytes: 377740163
> file data blocks allocated: 11278336921600
>  referenced 975937630208
> btrfs-progs v4.0

   That looks reasonably promising -- nothing seriously damaged that
btrfs check could find, at least.

> I tried googling the "open_ctree failed" error, but couldn't find any
> definite answers. Here's some additional info:

   "open_ctree failed" is a really generic error message,
unfortunately. Almost every case that leads to a failure to mount will
output that message, so there's no single solution you can find from
just that error. The "parent transid verify failed" is a much better
indication of what's happened here, and the small difference in
transid numbers would indicate that -orecovery might actually have a
chance of working.

   Hugo.

> uname -a:
> Linux Computer 4.2.0-22-generic #27-Ubuntu SMP Thu Dec 17 22:57:08 UTC
> 2015 x86_64 x86_64 x86_64 GNU/Linux
> 
> btrfs fi show:
> Label: none  uuid: b0486700-ff9f-4979-8735-257ff1428a0d
> Total devices 1 FS bytes used 290.37GiB
> devid    1 size 301.32GiB used 295.04GiB path /dev/sda8
> 
> Thanks in advance for any help,
> Radek

-- 
Hugo Mills             | Always be sincere, whether you mean it or not.
hugo@... carfax.org.uk |
http://carfax.org.uk/  |                                      Flanders & Swann
PGP: E2AB1DE4          |                                The Reluctant Cannibal

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