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? Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Is it true that "last known good" on Windows XP --- boots into CP/M?
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