Quota Implementation
Subsystems (2)
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.
-Arne
Quoted 27 lines · Arne Jansen
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.
Quoted 1 line
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.
Signature · 4 lines
=== 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? Quoted 4 lines · Hugo Mills
Quoted 3 lines · Arne Jansen
Hi,
If no one is already working on it, I'd like to take the Quota lock =
and
Quoted 4 lines
Quoted 4 lines
see how far I come.
Let me sketch out in short what I'm planning to do:=C2=A0- Quota will be subvolume based. Only the FS-trees and data ex=
tents
Quoted 2 lines
Quoted 2 lines
=C2=A0 =C2=A0will be accounted.
=C2=A0- Quota Groups can be defined. Every quota group can comprise =
any
Quoted 1 line
Quoted 1 line
=C2=A0 =C2=A0number of subvolumes. A subvolume can be assigned to an=
y number
Quoted 2 lines
Quoted 2 lines
=C2=A0 =C2=A0of quota groups.
=C2=A0- A Quota Group can account/limit the total amount of space th=
at is
Quoted 1 line
Quoted 1 line
=C2=A0 =C2=A0referenced by it and/or the amount of space that is exc=
lusively
Quoted 2 lines
Quoted 2 lines
=C2=A0 =C2=A0referenced (i.e. referenced by no other quota group). =C2=A0- With this it is possible to define a hierarchical quota that=
need
Quoted 2 lines
Quoted 2 lines
=C2=A0 =C2=A0not necessarily reflect the filesystem hierarchy. =C2=A0- It is also possible to decide for each snapshot if it should=
be
Quoted 1 line
Quoted 1 line
=C2=A0 =C2=A0accounted into the parent group. So in a scenario where=
each
Quoted 1 line
Quoted 1 line
=C2=A0 =C2=A0subvolume reflect a user home, it's possible to have so=
me snapshots
Quoted 1 line
Quoted 1 line
=C2=A0 =C2=A0accounted to the user and others not (e.g. the ones nee=
ded for system
Quoted 2 lines
Quoted 2 lines
=C2=A0 =C2=A0backups).
=C2=A0- Quota information will be stored in new records, possibly in=
a
Quoted 3 lines
Quoted 3 lines
=C2=A0 =C2=A0separate tree.
=C2=A0- It should be possible to change the Quota config and group =C2=A0 =C2=A0assignments online, though this might need a full re-sc=
an of the fs.
Quoted 5 lines
Quoted 3 lines
=C2=A0- It does NOT include any kind of user/group (UID/GID) quota.
Any addenda or arguments why it's impossible or insane welcome.
=C2=A0 There's a problem in that in some cases, it's possible to get =
into
Quoted 7 lines
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.
=C2=A0 If users can create their own subvolumes, then using the "excl=
usive
Quoted 6 lines
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.
=C2=A0 Getting out the bike-shed brush, I might suggest the use of so=
me
Quoted 3 lines
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 :)?
Regards,
Andrey
Quoted 5 lines
=C2=A0 Hugo.
--
=3D=3D=3D Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.=
org.uk =3D=3D=3D
Quoted 1 line
=C2=A0PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.=
org.uk
Quoted 1 line
=C2=A0 =C2=A0 =C2=A0 =C2=A0 --- Is it true that "last known good" on =
Windows XP ---
Quoted 1 line
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
=C2=A0 =C2=A0 =C2=A0 =C2=A0boots into CP/M?
Quoted 10 lines
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (GNU/Linux)iD8DBQFN6RAiIKyzvlFcI40RAkkQAKCAulO65dL1F/vaO7W20qJEAKuonwCghfvH XlliA+eCfmLmP/G0quVALe0=3D
=3Dm513
-----END PGP SIGNATURE-----
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Quoted 44 lines · Andrey Kuzmin
Quoted 43 lines · Hugo Mills
Quoted 27 lines · Arne Jansen
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.Quoted 1 line
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.
Quoted 6 lines
Quoted 4 lines
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
Quoted 26 lines
Regards,
AndreyQuoted 9 lines
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?Quoted 9 lines
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (GNU/Linux)iD8DBQFN6RAiIKyzvlFcI40RAkkQAKCAulO65dL1F/vaO7W20qJEAKuonwCghfvH XlliA+eCfmLmP/G0quVALe0=
=m513
-----END PGP SIGNATURE-------
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Quoted 28 lines · Hugo Mills
Quoted 27 lines · Arne Jansen
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.
Quoted 8 lines
Quoted 1 line
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.
I wouldn't prevent the deletion in A, but let go B over quota instead. Maybe a limit on exclusive use is of little practical use, but a tracking of it is very useful, as it is the space that will get freed if this subvol should get deleted. So it is an answer to the question 'how big is this snapshot?'.
Quoted 27 lines · 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.
Quoted 1 line
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
Quoted 28 lines · Johannes Hirte
Quoted 27 lines · 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.
Quoted 4 lines
Quoted 1 line
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?
Because it's already the simplest solution I can think of. The described scenarios are not arbitrary, I'm going to need all of them. Just having a subvolume limitation in the sense that the amount of referenced data is limited makes implementation of those impossible, even with user quota. Implementation with the proposed mechanisms would be very straightforward and wouldn't need any tricks. Btw, in my use case every user has the same UID.
Quoted 4 lines
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.
I currently have no use of user quotas, and sensibly implementing them in the presence of writable snapshots and cp --reflink would probably lead to a design similar to the above.
-Arne
Quoted 3 lines
regards,
Johannes