Frédéric Nass <frederic.nass@xxxxxxxxxxxxxxxx> writes: > Hello, > > I would like to use a cephfs snapshot as a read/write volume without having to > clone it first as the cloning operation is - if I'm not mistaken - still > inefficient as of now. This is for a data restore use case with Moodle > application needing a writable data directory to start. > > The idea that came to mind was to use overlayFS with cephfs set up as a > read-only lower layer and a writable local directory set up as an upper > layer. With this set up, any modifications to the read-only .snap/testsnap > directory would normally go to the upper directory making the snapshot directory > somehow writable to the Moodle application. While this works fine when a local > read-only filesystem is set up as the lower layer, it fails when cephfs is set > up as the lower layer. Any modifications to the .snap/testsnap tree in the > /cephfs-snap directory fails with an "Operation not supported". > > $ mkdir /cephfs /upperdir /workdir /cephfs-snap > > $ mount -t ceph 100.74.191.129:/volumes/group1/subvolume1/ /cephfs -o > name=admin,secretfile=/etc/ceph/admin.secret > > $ mount -t overlay overlay -o > redirect_dir=on,lowerdir=/cephfs/.snap/testsnap,upperdir=/upperdir,workdir=/workdir > /cephfs-snap > > $ ls /cephfs-snap > usr > > $ touch /cephfs-snap/foo.txt <---- writing outside the lowerdir > succeeds > > $ ls /cephfs-snap > foo.txt usr > > $ ls /usr/etc > > $ touch /cephfs-snap/usr/etc/foo <---- writing inside the lowerdir > fails > touch: impossible de faire un touch « /cephfs-snap/usr/etc/foo »: Opération non > supportée > > I tried to mount the whole cephfs tree read-only (-o ro), tried to disable ACLs > (-o noacl) as seen here [1] but of no help. Mounting with ceph-fuse didn't help > either. There's been a recent discussion about this here [2] between Greg and > Robert but with no real solution. I just commented on that bug tracker and, although I'm not really 100% sure, I suspect that the tmpfs on that system has been compiled without xattr support. > Did someone manage to do this? I couldn't reproduce you're problem. Is it possible that your upper dir doesn't support xatttrs either? Also, kernel client details would help. Cheers, -- Luis > > Regards, > > Frédéric. > > [1] https://blog.fai-project.org/posts/overlayfs/ > [2] https://tracker.ceph.com/issues/44821 > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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