On Thu, Jul 7, 2016 at 11:46 AM, M G Berberich wrote:
> Hello,
>
> On a filesystem with 40 G free space and 54 G used, ‘fstrim -v’ gave
> this result:
>
> # fstrim -v /
> /: 0 B (0 bytes) trimmed
>
> After running balance it gave a more sensible
>
> # fstrim -v /
> /: 37.3 GiB (40007368704 bytes) trimmed
>
> As far as I understand, fstrim should report any unused block to the
> disk, so its controller can reuse these blocks. I expected ’fstrim -v’
> to report about 40 G trimmed. The fact, that after balance fstrim
> reports a sensible amount of trimmed bytes leads to the conclusion,
> that fstrim on btrfs does not report unused blocks to the disk (as it
> should), but only the blocks of unused chunks. As the fstrim-command
> only does a ‘ioctl(fd, FITRIM, ))’ this seems to be a bug in the
> fstrim kernel-code.
> In the field this means, that without regularly running balance,
> fstrim does not work on btrfs.
hmm, yes indeed I see this as well:
# btrfs fi us /
Overall:
Device size: 55.00GiB
Device allocated: 46.55GiB
Device unallocated:8.45GiB
Device missing: 0.00B
Used: 39.64GiB
Free (estimated): 13.96GiB (min: 13.96GiB)
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 480.00MiB (used: 0.00B)
Data,single: Size:43.77GiB, Used:38.25GiB
/dev/sda1 43.77GiB
Metadata,single: Size:2.75GiB, Used:1.39GiB
/dev/sda1 2.75GiB
System,single: Size:32.00MiB, Used:16.00KiB
/dev/sda1 32.00MiB
Unallocated:
/dev/sda1 8.45GiB
# fstrim -v /
/: 9,3 GiB (10014126080 bytes) trimmed
# fallocate -l 5G testfile
# fstrim -v /
/: 4,3 GiB (4644130816 bytes) trimmed
Where the difference between 8.45GiB and 9,3 GiB comes from, I
currently don't understand.
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