On 03.06.2011 22:44, Andrey Kuzmin wrote:
On Fri, Jun 3, 2011 at 8:47 PM, Hugo Mills<hugo@xxxxxxxxxxxxx> wrote:
On Fri, Jun 03, 2011 at 06:24:41PM +0200, Arne Jansen wrote:
Hi,
If no one is already working on it, I'd like to take the Quota lock and
see how far I come.
Let me sketch out in short what I'm planning to do:
- Quota will be subvolume based. Only the FS-trees and data extents
will be accounted.
- Quota Groups can be defined. Every quota group can comprise any
number of subvolumes. A subvolume can be assigned to any number
of quota groups.
- A Quota Group can account/limit the total amount of space that is
referenced by it and/or the amount of space that is exclusively
referenced (i.e. referenced by no other quota group).
- With this it is possible to define a hierarchical quota that need
not necessarily reflect the filesystem hierarchy.
- It is also possible to decide for each snapshot if it should be
accounted into the parent group. So in a scenario where each
subvolume reflect a user home, it's possible to have some snapshots
accounted to the user and others not (e.g. the ones needed for system
backups).
- Quota information will be stored in new records, possibly in a
separate tree.
- It should be possible to change the Quota config and group
assignments online, though this might need a full re-scan of the fs.
- It does NOT include any kind of user/group (UID/GID) quota.
Any addenda or arguments why it's impossible or insane welcome.
There's a problem in that in some cases, it's possible to get into
a situation where you can't *delete* files because you're going over
quota. If I have two subvolumes that share most of their data
(e.g. one is a snapshot of the other), and both subvolumes have a
limit under the "exclusive use" clause, then deleting material from
subvolume A could cause subvolume B to go over quota.
If users can create their own subvolumes, then using the "exclusive
use" form is also pointless, because as a user, I can simply snapshot
(or otherwise CoW copy) all my data into a snapshot, and I then don't
pay for it. That one probably comes under the "admin shot himself in
the foot", though.
Getting out the bike-shed brush, I might suggest the use of some
name other than "quota", because inevitably people will think of
UID/GID-type quotas, and we've got enough confusingly-modified
terminology already. "Size bounds", "storage bounds", possibly?
Budget :)?
I wouldn't bother trying to coin a new term. Quota is already widely
in use for non-UID style quotas. ZFS has Filesystem Quotas, NetApp has
Tree Quotas (well, originally Quota Trees). So with calling them
Subvolume Quotas or Subvol Quotas I feel comfortable. This is distinct
enough from "User Quota".
-Arne
Regards,
Andrey
Hugo.
--
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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