Re: How to find/reclaim missing space in volume

[Hans van Kranenburg <hans@knorrie.org>]

Hi,

On 6/7/23 21:17, Marc MERLIN wrote:
> On Wed, Jun 07, 2023 at 10:12:30AM +0800, Qu Wenruo wrote:
>> For the ghost subvolumes, it can be confirmed with "btrfs ins dump-tree
>> -t root", then looking for ROOT_ITEMs with "refs 0".
>>
>> I'm not sure if it is the case.
>>
>> Another possible cause is extent bookends, this needs something like
>> btrfs quota to confirm, and not much we can do if there are snapshots.
>> (If no snapshots, it's possible to defrag and free up such bookend extents).
> 
> unfortunately the system rebooted overnight, so I lost the state where
> sync was hung.
> On the plus side, this seems to have fixed the issue:

Just a random hint... One possible situation in which a deleted
subvolume can't be freed up for real yet, is when there is a process
that still has an open file in it.

> sauron:/mnt/btrfs_pool2# btrfs fi usage -T .
> Overall:
>     Device size:		   1.04TiB
>     Device allocated:		 857.02GiB
>     Device unallocated:		 210.73GiB
>     Device missing:		     0.00B
>     Used:			 589.30GiB
>     Free (estimated):		 470.78GiB	(min: 365.42GiB)
>     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 845.00GiB 12.00GiB  16.00MiB   210.73GiB
> -- ----------------- --------- -------- --------- -----------
>    Total             845.00GiB  6.00GiB   8.00MiB   210.73GiB
>    Used              584.95GiB  2.18GiB 112.00KiB            
> sauron:/mnt/btrfs_pool2# df -h .
> Filesystem         Size  Used Avail Use% Mounted on
> /dev/mapper/pool2  1.1T  590G  471G  56% /mnt/btrfs_pool2
> 
> I know it's hard to say after the fact, but have you seen issues where snapshot delete
> space cleanup would get stuck and 
> btrfs subvolume sync `pwd`
> would hang forever (until reboot) ?

Hans