Re: [Cephfs] Can't get snapshot under a subvolume

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Hello Gürkan,

Indeed, by design, snapshots are only possible at the top of a
subvolume (which is invisible in a pod). This is deliberate, as
otherwise they would become a mechanism for quota evasion.

You can try CSI-level snapshots, which use cephfs-level snapshots
under the hood. Or, you can even try giving your pod a permission to
talk to the CSI driver, which would then make snapshots on its behalf,
but I don't know offhand how to do it.

In any case, please also try asking in Kubernetes forums. On Ceph
side, unfortunately, everything works as intended.

On Sat, Mar 1, 2025 at 2:58 AM <ceph@xxxxxxxxx> wrote:
>
> Hello all,
>
> We're getting a "Operation not permitted" error while trying to create a snapshot on the client. It is somehow related to previously-asked Pacific issue mentioned here: https://www.spinics.net/lists/ceph-users/msg67908.html
>
> We are on squid (19.2.1) and the given workaround seems to be only temporary. Anyway, here are some details about the issue:
>
> Cephx side:
>
> ```
> client.mount-update-production
>         key: ***
>         caps: [mds] allow rws fsname=production-cephfs path=/volumes/_nogroup/update-production
>         caps: [mon] allow r fsname=production-cephfs
>         caps: [osd] allow rw tag cephfs data=production-cephfs
> ```
>
> FS flags:
> ```
> ~> sudo ceph fs lsflags production-cephfs
>  joinable allow_snaps allow_multimds_snaps
> ```
>
> I got the path via following command:
> ```
> ~> sudo ceph fs subvolume getpath production-cephfs update-production
> /volumes/_nogroup/update-production/e155ba30-d201-4653-be3f-86533324ee5f
> ```
>
> And mounted to client with mentioned key:
> ```
> ~> mount | grep ceph
> mount-update-production@00000000-0000-0000-0000-000000000000.production-cephfs=/volumes/_nogroup/update-production/e155ba30-d201-4653-be3f-86533324ee5f on /opt/aptly/.aptly type ceph (rw,noatime,name=mount-update-production,secret=<hidden>,acl,mon_addr=[multiple mon addresses here])
> ```
>
> Everything works flawlessly. Yet, when we want to get a snapshot:
> ```
> /opt/aptly/.aptly/pool/9c/0b ~> sudo mkdir .snap/test
> mkdir: cannot create directory ‘.snap/test’: Operation not permitted
> ```
>
> If I mount the whole FS with admin rights and run `setfattr -n ceph.dir.subvolume -v 0` for _all_ directories of following path one by one: /volumes/_nogroup/update-production/e155ba30-d201-4653-be3f-86533324ee5f, then it is solving the issue. But it does not last; not sure what is triggering it again, but if I try snapshotting anything next day, getting the same "Operation not permitted" error again.
>
> Is there something I can try, or am I missing something obvious?
>
> Thanks,
> Gürkan
> _______________________________________________
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-- 
Alexander Patrakov
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