Re: btrfs-transacti causing IO problem to btrfs (skinny-metadata?)

[Martin <m_btrfs@ml1.co.uk>]

On 25/03/15 08:29, Ian Gordon wrote:
> 
> Hello,
> 
> I have a btrfs filesystem which has been working ok for about 90days,
> but on Monday it become very slow (takes about 6hours to rsync backup a
> 3GB Ubuntu server - despite minimal changes from previous backup). I
> noticed, that even with no processes reading or writing to the
> filesystem, that btrfs-transaci was writing to the disk (averaging at
> about 5MB/s) for a few hours before stopping until I wrote to the
> filesystem again and then the process would repeat.
> 
> The btrfs filesystem uses skinny-metadata and is mounted with relatime
> It has 744 subvolumes (of which about 700 are readonly snapshots)
> 
> Any ideas? Is there some sort of cleanup getting automatically run in
> the background?

Is that btrfs system formatted with a previous kernel (pre-
skinny-metadata) and is now being used with a kernel that newly has
skinny-metadata enabled by default?...


I've stumbled across a bug/change/patch listed for a mixed pre/post
skinny-metadata whereby you get to see lots of csum errors in the logs...

For one 16TB btrfs raid1 system that brought things down to read-only...


I'm now on kernel 3.18.9, and Btrfs v3.18.2. Presently copying the
latest data onto a backup before trying a scrub! :-)

LOTs of:

kernel: parent transid verify failed on 5992676900864 wanted 70743 found
70709
kernel: parent transid verify failed on 5992676900864 wanted 70743 found
70709
kernel: BTRFS info (device sdj): no csum found for inode 50675726 start
16384
kernel: BTRFS info (device sdj): csum failed ino 50675726 off 0 csum
42383870 expected csum 0
kernel: BTRFS info (device sdj): csum failed ino 50675726 off 4096 csum
815939273 expected csum 0

and variations seen.

(Or advice for that one welcomed! ;-) )


Cheers,
Martin