Re: Report correct filesystem usage / limits on BTRFS subvolumes with quota

[Andrei Borzenkov <arvidjaar@gmail.com>]

12.08.2018 10:04, Andrei Borzenkov пишет:
> 
> On ZFS snapshots are contained in dataset and you limit total dataset
> space consumption including all snapshots. Thus end effect is the same -
> deleting data that is itself captured in snapshot does not make a single
> byte available. ZFS allows you to additionally restrict active file
> system size ("referenced" quota in ZFS) - this more closely matches your
> expectation - deleting file in active file system decreases its
> "referenced" size thus allowing user to write more data (as long as user
> does not exceed total dataset quota). This is different from btrfs
> "exculsive" and "shared". This should not be hard to implement in btrfs,
> as "referenced" simply means all data in current subvolume, be it
> exclusive or shared.
> 

Oops, actually this is exactly what "referenced" quota is. Limiting
total subvolume + snapshots is more difficult, as there is no inherent
connection between qgroups of source and snapshot nor any built-in way
to include snapshot qgroup in some common total qgroup when creating
snapshot.