[Linux-cluster] Quorum Disk on 2 nodes out of 4?

[Karl Podesta]

Hi there, 

Is it possible to have a quorum disk, applicable only to 2 nodes
out of a 4 node cluster? (i.e. with the other 2 nodes not connected
to the shared quorum disk storage, or not affected by failover or
service operation on the 2 nodes that are sharing a disk?)

I have encountered the following scenario with a 4-node cluster:
(using RHEL 4.8)

=============
Nodes 1 & 2: 
Acting as database nodes, sharing a database service between them 
(there is a shared disk with an ext3 partition that is only mounted
on one node at a time)

Node 3: 
Standalone network service, with an IP address. No shared storage.
Network service uses the database on nodes 1 & 2. 

Node 4: 
Standalone network service, with an IP address. No shared storage. 
Network service uses the database on nodes 1 & 2.
=============

Failover domains are configured appropriately (one for Nodes 1 & 2, 
one for Node 3, one for Node 4). The owner of the cluster would like
to introduce a shared quorum disk to the two DB nodes, to ensure that
the DB service basically fails over between the DB nodes, in the case
where shared disk access is lost (i.e. card or cable failure) on the
active DB node. 

This architecture should really be two clusters, right? One separate
cluster for DB, and another cluster (even if) for the network apps?
I gather it has been configured this way from a desire to logically
keep all of these services together in the one "system". 

Apologies if a similar question has been asked in the past, any inputs, 
thoughts, or pointers welcome. 

Karl

-- 
Karl Podesta