Howto fix uncorrectable errors on single disk (error details: csum=1)

Howto fix uncorrectable errors on single disk (error details: csum=1)

[Tim Janik]

Hey All.

After a power failure, I encountered a checksum error on a backup disk,
reported by btrfs scrub. I failed to identify any particular file
affected by the reported "error at logical 250492215296".

How do I get rid of the corruption reported by btrfs scrub?
Since this is a backup disk, deleting any affected file or snapshot
would be fine.

uname -a
Linux dozer 4.15.0-43-generic #46-Ubuntu SMP Thu Dec 6 14:45:28 UTC 2018 x86_64
x86_64 x86_64 GNU/Linux

btrfs --version
btrfs-progs v4.15.1

btrfs fi show
Label: 'BtrfsBackups'  uuid: bacbfa3e-b200-4ed4-888c-e2cdf5ca3ed8
        Total devices 1 FS bytes used 2.23TiB
        devid    1 size 3.64TiB used 2.58TiB path /dev/mapper/d6

btrfs fi df /backup
Data, single: total=2.54TiB, used=2.23TiB
System, DUP: total=64.00MiB, used=368.00KiB
Metadata, DUP: total=18.00GiB, used=5.49GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

dmesg
[278033.156632] BTRFS info (device dm-2): use zstd compression, level 0
[278033.156635] BTRFS info (device dm-2): enabling auto defrag
[278033.156637] BTRFS info (device dm-2): disk space caching is enabled
[278033.156638] BTRFS info (device dm-2): has skinny extents
[278033.250808] BTRFS info (device dm-2): bdev /dev/mapper/d6 errs: wr 0, rd 0,
flush 0, corrupt 4, gen 0
[296190.630316] BTRFS error (device dm-2): bdev /dev/mapper/d6 errs: wr 0, rd 0,
flush 0, corrupt 5, gen 0
[296190.630326] BTRFS error (device dm-2): unable to fixup (regular) error at
logical 250492215296 on dev /dev/mapper/d6
[300491.284115] perf: interrupt took too long (4959 > 4958), lowering
kernel.perf_event_max_sample_rate to 40250
[321935.768710] BTRFS info (device dm-2): use zstd compression, level 0
[321935.768714] BTRFS info (device dm-2): enabling auto defrag
[321935.768716] BTRFS info (device dm-2): disk space caching is enabled
[321935.768717] BTRFS info (device dm-2): has skinny extents
[321935.866552] BTRFS info (device dm-2): bdev /dev/mapper/d6 errs: wr 0, rd 0,
flush 0, corrupt 5, gen 0

btrfs scrub status /backup/
scrub status for bacbfa3e-b200-4ed4-888c-e2cdf5ca3ed8
        scrub started at Tue Jan  8 05:01:02 2019 and finished after 04:16:48
        total bytes scrubbed: 2.24TiB with 1 errors
        error details: csum=1
        corrected errors: 0, uncorrectable errors: 1, unverified errors: 0

btrfs inspect-internal logical-resolve 250492215296 /backup/
<NO-OUTPUT>


-- 
Yours sincerely,
Tim Janik

https://testbit.eu/timj
Free software author