Re: How to find/reclaim missing space in volume

[Andrei Borzenkov <arvidjaar@gmail.com>]

On 06.06.2023 04:46, Marc MERLIN wrote:
> On Mon, Jun 05, 2023 at 08:00:02PM +0300, Andrei Borzenkov wrote:
>> 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# btrfs fi usage -T .
> Overall:
>      Device size:		   1.04TiB
>      Device allocated:		 890.02GiB
>      Device unallocated:		 177.73GiB
>      Device missing:		     0.00B
>      Used:			 851.85GiB
>      Free (estimated):		 211.93GiB	(min: 123.07GiB)
>      Data ratio:			      1.00
>      Metadata ratio:		      2.00
>      Global reserve:		 512.00MiB	(used: 0.00B)
> 
>                       Data      Metadata System
> Id Path              single    DUP      DUP       Unallocated
> -- ----------------- --------- -------- --------- -----------
>   1 /dev/mapper/pool2 878.00GiB 12.00GiB  16.00MiB   177.73GiB
> -- ----------------- --------- -------- --------- -----------
>     Total             878.00GiB  6.00GiB   8.00MiB   177.73GiB
>     Used              843.79GiB  4.03GiB 128.00KiB
> 
>>> 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).
> 
> Right, I did check/know that the snapshots shared the same data, but it
> doens't hurt to confirm:
> 
> sauron:/mnt/btrfs_pool2# btrfs filesystem du -s *
>       Total   Exclusive  Set shared  Filename
>   597.57GiB    20.00KiB   588.75GiB  varchange2
>   597.57GiB     4.00KiB   588.75GiB  varchange2_ggm_daily_ro.20230605_09:59:26
>   597.57GiB       0.00B   588.75GiB  varchange2_last
>   597.57GiB     4.00KiB   588.75GiB  varchange2_minly.20230605_17:30:33
>   597.57GiB       0.00B   588.75GiB  varchange2_minly.20230605_17:35:32
>   597.57GiB       0.00B   588.75GiB  varchange2_minly.20230605_17:40:32
>   597.57GiB     4.00KiB   588.75GiB  varchange2_minly.20230605_17:45:32
>   597.57GiB     4.00KiB   588.75GiB  varchange2_minly.20230605_17:50:32
>   597.57GiB     4.00KiB   588.75GiB  varchange2_minly.20230605_17:55:32
>   597.57GiB       0.00B   588.75GiB  varchange2_minly.20230605_18:00:32
>   597.57GiB       0.00B   588.75GiB  varchange2_minly.20230605_18:05:32
>   597.57GiB     8.00KiB   588.75GiB  varchange2_minly.20230605_18:10:32
>   597.57GiB    16.00KiB   588.75GiB  varchange2_ro.20230605_10:01:40
>   597.57GiB    12.00KiB   588.75GiB  varchange2_ro.20230605_11:01:31
>   597.57GiB     4.00KiB   588.75GiB  varchange2_ro.20230605_13:01:28
>   597.57GiB     4.00KiB   588.75GiB  varchange2_ro.20230605_14:01:30
>   597.57GiB     4.00KiB   588.75GiB  varchange2_ro.20230605_15:01:29
>   597.57GiB     4.00KiB   588.75GiB  varchange2_ro.20230605_16:01:32
>   597.57GiB     4.00KiB   588.75GiB  varchange2_ro.20230605_17:01:31
>   597.57GiB       0.00B   588.75GiB  varchange2_ro.20230605_18:02:02
> sauron:/mnt/btrfs_pool2# df -h .
> Filesystem         Size  Used Avail Use% Mounted on
> /dev/mapper/pool2  1.1T  853G  212G  81% /mnt/btrfs_pool2
> 
> 

Well, I have had it once, there were deleted but not freed subvolumes

https://lore.kernel.org/linux-btrfs/ecd46a18-1655-ec22-957b-de659af01bee@gmx.com/T/