[DRBD-user] Display linstor's backing device

[Roland Kammerer]

On Mon, Jan 07, 2019 at 02:50:30PM +0100, Julien Escario wrote:
> Hello,
> We're using ZFSThin as backend for our Linstor cluster. Nothing fancy.
> 
> I'm trying to set up a backup with ZFS snapshots and zfs send/receive.

LINSTOR can take snapshots. Shipping these with zfs send/receive can make
sense. Don't take the snapshots yourself. LINSTOR makes sure things are
fine when it takes these. Taking "distributed snaphosts" is, hm, funny.

> First : is this a bad idea ? I know DRBD integrate his own snapshot
> system (LVM only ?) but it can't be exported to a non-DRBD system as-is
> AFAIK.

w00t? Do not mess with the backing devices directly. Never. Not even for
things like a fsck. Things are not consistent anymore if DRBD does not
see the changes. Besides that, you should be able to use the snapshots
taken by LINSTOR and then shipped and access the data without DRBD. The
snapshot is taken from the backing device (but LINSTOR is "careful" when
and how). And then it is a snapshot as usual. For example if you have a
DRBD disk that has a FS on it, you can, in the very worst case, leave
DRBD out of the picture, because for the FS it should not matter. It
finds its meta-data at the beginning of the device, but it will not care
about the DRBD meta-data at the end.

In your case you maybe want to take the snapshot with LINSTOR and then
mount the snapshot read-only and rsync the data to the backup? Then you
have a "plain text data" backup.

> So, main question : is there a linstor command to get the 'grepable'
> backend device for a resource on a host ?

Maybe some machine readable output command + json parsing? But so far
there is IMO no real "scriptable output". You have ascii/utf8 tables or
json.

> I tried some lisntor commands without success. Perhaps with a command
> from drbd-utils ?

drbdadm sh-ll-dev resname

Don't hurt yourself :)

Regards, rck