Luis,
I gave RHEL 8 and kernel 4.18 a try and it's working perfectly! \o/
Same commands, same mount options. Does anyone know why and if there's
any chances I can have this working with CentOS/RHEL 7 and 3.10 kernel?
Best regards,
Frédéric.
Le 09/11/2020 à 15:04, Frédéric Nass a écrit :
Hi Luis,
Thanks for your help. Sorry I forgot about the kernel details. This is
latest RHEL 7.9.
~/ uname -r
3.10.0-1160.2.2.el7.x86_64
~/ grep CONFIG_TMPFS_XATTR /boot/config-3.10.0-1160.2.2.el7.x86_64
CONFIG_TMPFS_XATTR=y
upper directory /upperdir is using xattrs
~/ ls -l /dev/mapper/vg0-racine
lrwxrwxrwx 1 root root 7 6 mars 2020 /dev/mapper/vg0-racine -> ../dm-0
~/ cat /proc/fs/ext4/dm-0/options | grep xattr
user_xattr
~/ setfattr -n user.name -v upperdir /upperdir
~/ getfattr -n user.name /upperdir
getfattr: Suppression des « / » en tête des chemins absolus
# file: upperdir
user.name="upperdir"
Are you able to modify the content of a snapshot directory using
overlayfs on your side?
Frédéric.
Le 09/11/2020 à 12:39, Luis Henriques a écrit :
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
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