Re: Quota Implementation

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On Friday 03 June 2011 18:24:41 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.

What's the benefit of this complexity? Why not a more simple quota/reservation 
per subvolume? The semantics you described, can be achived by user/group 
quotas too. And we need them anyway. Perhaps this can be implemented together, 
reusing the code. Then we have the question if user/group quotas are per 
filesystem or per subvolume.

regards,
  Johannes
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