Hi James,
this is an interesting discussion for me. This raises 2 questions for my
understanding of the concept:
1) do you mean snapshots are not taken in account for quotas ? A user
can remove files after a snapshot to retrieve some storage ?
2) in a cephfs context using subvolumes per user require a mount point
for each user on the clients ? Or many users folders with different
quota can coexist in the subvolume ?
Patrick (Ceph beginner not using subvolumes yet)
Le 20/06/2025 à 10:24, Alexander Patrakov a écrit :
Hello James,
The special thing about subvolumes is that you can only take snapshots at
their root but not inside. This is a security feature: give a subdirectory
of a subvolume to a user, set the quota on the subvolume, and you can be
sure that the user will not be able to circumvent the quota by creating new
snapshots in the area he has access to.
On Fri, Jun 20, 2025 at 3:54 PM James Tocknell <james.tockn...@mq.edu.au>
wrote:
Hi All
Possibly a dumb question, but given with cephfs you can apply quotas to
arbitrary directories, snapshot arbitrary directories, assign arbitrary
directories to pools etc. what is special/different about subvolumes, and
why would I want to use them (and more importantly, not want to use them)?
I guess the only thing I can see could be around where the extended
attributes are assigned (with the two-level directory structure enabling
setting a quota while not allowing read access to the directory above,
based on looking at the cephfs CSI?), but I feel I'm missing something
obvious.
The specific usecase I'm looking at is evaluating using just quotas vs
subvolumes for team shares (to ensure that each team only uses the amount
of storage they require), but in general I'm trying to understand
subvolumes.
Regards
James
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