[Linux-cluster] GNBD/GFS/cluster questions

[Chris Picton]

Hi all

I have a question regarding gnbd and clustering.

I currently have two servers (store1 and store2) sharing a block device 
(/dev/sdc) via drbd.

The 'Primary' server exports this device via gnbd, and the export fails 
over along with the drbd primary node.
A third server (gfs1) imports the gnbd device (which is part of an lvm) 
and mounts a gfs2 filesystem on it.

I currently do not want to run drbd in primary/primary mode, as I have 
read that there are potentially some performance issues with this.

I have written two custom scripts to handle the drbd and gnbd resource 
failover.

If I am not going to mount the gfs2 filesystem on store1, or store2, can 
I create a 'private' cluster between only those two machines, with their 
own dlm, or do all of the other machines (only gfs1 in this example) 
which will be mounting the gfs filesystem have to use the same dlm, and 
be part of the same cluster?  If I were to share the drbd device via 
iscsi, then I see no need for the importing devices to even be aware 
that the device is being exported by a cluster of machines - does this 
hold true for gnbd as well?

Is there any benefit of have *all* my servers in the same cluster, or 
can I split them up into smaller logically separated clusters.

Eg, if I add another two servers, with a failover gnbd export, do they 
also have to be part of the same global cluster, if they will be sharing 
the gnbd device into the same clvm?  Or can they have their own 
'private' cluster between themselves as well?

Regards

Chris