[Linux-cluster] Quorum question / split brain paranoia

[Christopher Barry]

Greetings all,

I'm building a 6-node hybrid virtual cluster, and would like a little
advice about quorum concepts, with the goal being functioning of at
least one virtual node, on one physical box, and the complete inability
of split-brain occurring.

I have Two Physical machines (PM) that will host many virtual machines,
however only three VMs per PM will actually be members of the cluster.

_Each_ PM is running VMware ESX 3, with: 
* 3 es4ud5 cluster node VMs
* director node VM in an Active/Passive config
* various other, non-cluster nodes, out of scope.

The diagram of one physical machine with the relevant VMs, virtual
switches and virtual wiring can be seen below.

Each PM is a mirror image of the other:
  (view this as a fixed font)
+------------------------------+
|     PHYSICAL ESX BOX         |
| +-----------------------+    |
| |   VM Cluster Node1    |--+ |
| +-----------------------+  | |
| +-----------------------+  | |
| |   VM Cluster Node2    |--+ |
| +-----------------------+  | |
| +-----------------------+  | |
| |   VM Cluster Node3    |--+ |
| +-----------------------+  | |
|             +---+---+------' |
| +-----------|---|---|---+    |
| |Cluster Virtual Switch |--+ |
| +--------------|--------+  | |
|  10.0.1.0/24   +-----+     | |
| +--------------------|--+  | |
| | Director VM Node (NAT)|  | |
| +---|-------------------+  | |
|   +-'   10.0.0.0/24        | |
| +-|---------------------+  | |
| |Director Virtual Switch|  | |
| +----------|------------+  | |
|            |               | |
|            |       +-------' |
+===[fc0]===[e0]===[e1]========+
      |      |       |
    to SAN   |       `---> x-over cable to mirror box
           To LAN

The cluster nodes will run GFS, the director will not. Only one director
will be active with a VIP, load will balance across all 6 VMs. The
crossover will actually have VLANs on it that will allow a separate
heartbeat net, but it was getting a bit tricky with ASCII art ;)

Can anyone see any issues that may arise where quorum could create a
split brain scenario? What would be the best way to approach votes, etc.
here?


Thanks all for your time.




-- 
Regards,
-C

Christopher Barry
Systems Engineer, Principal
QLogic Corporation
780 Fifth Avenue, Suite 140
King of Prussia, PA   19406
o/f: 610-233-4870 / 4777
  m: 267-242-9306