Re: fsck: to repair or not to repair

[Nikolaus Rath <Nikolaus@rath.org>]

On May 11 2016, Nikolaus Rath <Nikolaus@rath.org> wrote:
> Hello,
>
> I recently ran btrfsck on one of my file systems, and got the following
> messages:
>
> checking extents
> checking free space cache
> checking fs roots
> root 5 inode 3149867 errors 400, nbytes wrong
> root 5 inode 3150237 errors 400, nbytes wrong
> root 5 inode 3150238 errors 400, nbytes wrong
> root 5 inode 3150242 errors 400, nbytes wrong
> root 5 inode 3150260 errors 400, nbytes wrong
> [ lots of similar message with different inode numbers ]
> root 5 inode 15595011 errors 400, nbytes wrong
> root 5 inode 15595016 errors 400, nbytes wrong
> Checking filesystem on /dev/mapper/vg0-nikratio_crypt
> UUID: 8742472d-a9b0-4ab6-b67a-5d21f14f7a38
> found 263648960636 bytes used err is 1
> total csum bytes: 395314372
> total tree bytes: 908644352
> total fs tree bytes: 352735232
> total extent tree bytes: 95039488
> btree space waste bytes: 156301160
> file data blocks allocated: 675209801728
>  referenced 410351722496
> Btrfs v3.17
>
>
> Can someone explain to me the risk that I run by attempting a repair,
> and (conversely) what I put at stake when continuing to use this file
> system as-is?
 
To follow-up on this: after finding out which files were affected (using
btrfs inspect-internal), I was able to fix the problem without using
btrfsck by simply copying the data, deleting the file, and restoring it:

cat affected-files.txt | while read -r name; do
rsync -a "${name}" "/backup/location/${name}"
rm -f "${name}"
cp -a "/backup/location/${name}" "${name}"
done

(I used rsync to avoid cp making use of reflinks). After this procedure,
btrfschk reported no more problems.


Best,
-Nikolaus

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