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

[Fabio M. Di Nitto]

Karl Podesta wrote:
> Hi there, 
> 
> Is it possible to have a quorum disk, applicable only to 2 nodes
> out of a 4 node cluster?

No. The prerequisite for qdisk to work is for all nodes in a cluster to
have it running at the same time.

> This architecture should really be two clusters, right? One separate
> cluster for DB, and another cluster (even if) for the network apps?

Yes and no. By splitting the 4 nodes cluster in 2x2nodes clusters will
only help partially.

The cluster with qdisk will be ok because qdisk will act as tie breaker
for fencing/quorum, but the other 2 nodes cluster (for network services)
will require other kind of attentions to avoid fencing races.

> 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. 

Ideally you would find a way to plug the storage into the 2 nodes that
do not have it now, and then run qdisk on top.

At that point you can also benefit from "global" failover of the
applications across all the nodes.

Fabio