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

[Mohr, Rick]

Peter,

You might want to take a look at this: https://www.opensfs.org/wp-content/uploads/2017/06/Wed06-CroweTom-lug17-ost_data_migration_using_ZFS.pdf

It's a few years old, but it shows how IU used zfs send/receive to copy data from osts.  I worked with someone several years ago to do basically the same procedure to make incremental copies of mdt data when we were attempting to switch over to a new mds server.  You don't need to unmount lustre in order to do the incremental backups. 

--Rick



On 5/18/23, 9:38 AM, "lustre-discuss on behalf of Peter Grandi via lustre-discuss" <lustre-discuss-bounces at lists.lustre.org <mailto:lustre-discuss-bounces at lists.lustre.org> on behalf of lustre-discuss at lists.lustre.org <mailto:lustre-discuss at lists.lustre.org>> wrote:


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 :-).


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