Re: How to find/reclaim missing space in volume

[Marc MERLIN <marc@merlins.org>]

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:

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) ?

Thanks,
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
 
Home page: http://marc.merlins.org/                       | PGP 7F55D5F27AAF9D08