Re: Kernel 5.4 - BTRFS FS shows full with about 600 GB Free ?

Qu Wenruo
2019-12-21T12:00:14Z

On 2019/12/21 下午6:59, Swâmi Petaramesh wrote:
> Hi list,
>
> After writing files and snapshots WITHOUT errors on an external BTRFS FS
> with 500+ GB of free space, using kernel 5.4.5-arch1-1, I dismount the
> FS then remount it normally, and then it says the FS has 0 space free
> left !
>
> Checking the disk on another machine with
>
> [moksha ~]# uname -r
> 5.4.2-1-MANJARO
>
> And... How can this be ?
>
> root@moksha:~# df -h /run/media/myself/MyVolume
> Filesystem           Size  Used Avail Use% Mounted on
> /dev/mapper/luks-xxxxxxxxx-yyyy-zzzz-tttt-wwwwwww   1,9T 1,2T     0 100%
> /run/media/myself/MyVolume

A known regression introduced in v5.4.

The new metadata over-commit behavior conflicts with an existing check
in btrfs_statfs().
It is completely a runtime false behavior, and had *no* other bad effect.

If you feel like to address it with off-tree patch, there is a quick
patch to address it:
https://patchwork.kernel.org/patch/11293419/

>
> root@moksha:~# btrfs fi sh
> Label: 'MyVolume'  uuid: xxxxxxxxx-yyyy-zzzz-tttt-wwwwwww
>         Total devices 1 FS bytes used 1.19TiB
>         devid    1 size 1.82TiB used 1.20TiB path
> /dev/mapper/luks-xxxxxxxxx-yyyy-zzzz-tttt-wwwwwww
>
> root@moksha:~# btrfs fi df /run/media/myself/MyVolume
> Data, single: total=1.18TiB, used=1.18TiB
> System, DUP: total=8.00MiB, used=160.00KiB
> Metadata, DUP: total=7.00GiB, used=6.88GiB
> GlobalReserve, single: total=512.00MiB, used=0.00B
>
> root@moksha:~# umount /run/media/myself/MyVolume
>
> root@moksha:~# btrfs check
> /dev/mapper/luks-xxxxxxxxx-yyyy-zzzz-tttt-wwwwwww
> Opening filesystem to check...
> Checking filesystem on /dev/mapper/luks-xxxxxxxxx-yyyy-zzzz-tttt-wwwwwww
> UUID: xxxxxxxxx-yyyy-zzzz-tttt-wwwwwww
> [1/7] checking root items
> [2/7] checking extents
> [3/7] checking free space cache
> [4/7] checking fs roots
>
> (Still running since a while, no errors...)

Running a fsck is always a good behavior, although in this case, it
shouldn't cause any corruption.

Thanks,
Qu
>
> TIA for any help.
>
> Kind regards.
>