Re: How to find/reclaim missing space in volume

[Andrei Borzenkov <arvidjaar@gmail.com>]

On 05.06.2023 19:26, Marc MERLIN wrote:
> I have this:
> sauron [mc]# df -h .
> Filesystem         Size  Used Avail Use% Mounted on
> /dev/mapper/pool2  1.1T  853G  212G  81% /mnt/btrfs_pool2
> sauron [mc]# btrfs fi show .
> Label: 'btrfs_pool2'  uuid: fde3da31-67e9-4f88-b90d-6c3f6becd56a
> 	Total devices 1 FS bytes used 847.89GiB
> 	devid    1 size 1.04TiB used 890.02GiB path /dev/mapper/pool2
> sauron [mc]# btrfs fi df .
> Data, single: total=878.00GiB, used=843.85GiB
> System, DUP: total=8.00MiB, used=128.00KiB
> Metadata, DUP: total=6.00GiB, used=4.04GiB
> GlobalReserve, single: total=512.00MiB, used=0.00B
> 

btrfs filesystem usage -T is usually more useful than both the above 
commands.

> 
> sauron:/mnt/btrfs_pool2# du -sh *
> 599G	varchange2
> 598G	varchange2_ggm_daily_ro.20230605_07:57:43
> 4.0K	varchange2_last
> 599G	varchange2_ro.20230605_08:01:30
> 599G	varchange2_ro.20230605_09:01:43
> 
> I'm confused, the volumes above are snapshots with mostly the same data
> (made within the last 2 hours) and I didn't delete any data in the FS
> (they are mostly identical and used for btfrs send/receive)
> 
> Why do they add up ot 600GB, but btrfs says 847FB is used?
> 

Each subvolume references 600G but it does not mean they are the same 
600G. If quota is enabled, "btrfs quota show" may provide some more 
information, otherwise "btrfs filesystem du" shows shared and exclusive 
space (you need to pass all subvolumes in question to correctly compute 
shared vs exclusive).