[lustre-discuss] ZFS zpool/filesystem operations while mounted with '-t lustre'

[Peter Grandi]

I have a Lustre 2.15.2 instance "temp01" on ZFS 2.1.5 (on EL8), and I 
just want to backup the MDT of the instance (I am mirroring the data on 
two separate "pools" of servers).

The "zpool" is called "temp01_mdt_000" and so is the filesystem, so the 
'/etc/fstab' mount line is (I have set legacy ZFS mount-points):

> temp01_mdt_000/temp01_mdt_000 /srv/temp01/temp01_mdt_000 lustre defaults,noatime,auto 0 0

As usual '/srv/temp01/temp01_mdt_000' is opaque (no access permissions) 
when mounted as 'lustre', but anyhow I would like to backup a snapshot 
of it, using 'zfs send'.

If I use 'zpool list' and 'zfs list' I see the relevant details even if 
it is mounted as 'lustre'. If I un-mount it and re-mount it as 'zfs' it 
looks ordinary, but I would rather not do that.

In theory, however it is mounted, I should be able to (suitably preceded 
by 'lctl barrier_freeze') create a snapshot for it, and mount that as 
'zfs' to some other mount-point and then 'zfs send' that.

Before doing it on a live Lustre instance (I can't easily afford to 
setup a test Lustre instance in the short run) I would like some 
confirmation that this is meant to work ideally by someone who does it 
routinely :-).