Hi John,

> 2 SLES 12 storage hosts with DRBD in primary/primary mode. Setup ISCSI targets on these 2 storage nodes on multiple paths
> [...]
> What do you think?

in my opinion it's still better to avoid primary/primary configurations, for operational stability reasons.

Personally, I'd set up the two storage servers with multiple DRBD resources, i.e. one per virtual disk, and run these in primary/secondary mode. Each of these can be handled via Pacemaker, together with activating each activated DRBD resource in the iSCSI target.

Going that route, you might see the following benefits:

- simpler design from the storage resource's operational point of view (albeit having more complex operations when migrating storage resources between nodes - but only at that point in time, not for every read/write request)

- trouble with single DRBD resources would only affect a single VM

- no OCFS2 overhead (cluster-wide communications), and you could even avoid file system overhead at the storage server completely (exporting the DRBD resource, rather than a file on it)

- you'd have load balancing at the storage server level, rather than trying to balance at the multipath layer

- easier growth for increased storage demand - you could place new DRBD resources on *any* storage of the servers, no need to grow the OCFS2 filesystem.

You'd have a read/write delay when migrating the "primary" from one storage node to the other, but that would likely get covered by retries and multipath handling.

I've yet to run something along those lines via iSCSI, my practical experiences with this are via Fiber Channel with NPIV.

Regards,
J