Re: cannot use btrfs for nfs server

Chris Murphy
2021-07-10T22:17:54Z

On Sat, Jul 10, 2021 at 12:56 AM Ulli Horlacher
<framstag@rus.uni-stuttgart.de> wrote:

> root@tsmsrvj:# snaprotate -v test 5 /data/fex/spool
> $ btrfs subvolume snapshot -r /data/fex/spool /data/fex/spool/.snapshot/2021-07-10_0849.test
> Create a readonly snapshot of '/data/fex/spool' in '/data/fex/spool/.snapshot/2021-07-10_0849.test'

I think this might be the source of the problem. Nested snapshots are
not a good idea, it causes various kinds of confusion. It's not any
different if you do an LVM snapshot and nest a bind mount of one file
system in another. I have no idea how NFS works but it sounds to me
it's getting confused when finding the same file system inodes
multiple times and that's just what happens with snapshots. Whether
Btrfs or some other snapshotting mechanism.

> We cannot move the snapshots to a different directory. Our workflow
> depends on snaprotate:
>
> http://fex.belwue.de/linuxtools/snaprotate.html

OK does the problem happen if you have no nested snapshots (no nested
subvolumes of any kind) in the NFS export path? If the problem doesn't
happen, then either the tool you've chosen needs to be enhanced so it
will create snapshots somewhere else, which Btrfs supports, or you
need to find another tool that can.

--
Chris Murphy