Comparison of Quorate and Resource Driven

The resource driven approach has several key benefits over the quorate approach:

1. the cluster layer can be thinner and simpler. This is not a direct advantage. However, the HA saying is ``complexity is the enemy of availability'', so the simpler your HA harness is, the more likely it is to function correctly under all failure scenarios.

2. recovery proceeds immediately without waiting for a quorum (or even a full communication set) to form.

3. Recoveries on different nodes, by virtue of the independence of the hierarchies, may be effected in parallel leading to faster overall cluster recovery.

4. May form independent subclusters: In the case where a cluster is totally partitioned, both partitions may recover hierarchies in a resource driven cluster; in a quorate cluster, only one partition may form a viable cluster.

5. recoverability is possible down to last man standing: As long as any nodes remain (and they can reach the resources necessary to the hierarchy) recovery may be effected. In a quorate cluster, recovery is no longer possible when the remaining nodes in a cluster lose quorum (either because too many votes have been lost, or because they can no-longer make contact with the tie breaker).

There are also several disadvantages:

1. For the paradigm to work, own-ability is a required property of at least one resource in a hierarchy. For some hierarchies (notably those not based on shared discs, like replicated storage) this may not be possible.

2. Some services exported from a cluster (like thinks as simple as cluster instance identity number) require a global state which a resource driven cluster does not have. Therefore, the cluster services API of a resource driven cluster is necessarily much less rich than for a quorate cluster.

3. The very nature of the simultaneous multi-node parallel recovery may cause a cluster resource crunch (too many things going on at once).

4. Since each node no-longer has a complete view of the cluster as a whole, administration becomes a more complex problem since the administrative tool must now build up its own view of the cluster from the information contained in the individual nodes.

However, the prime advantages of simplicity (Less cluster glue layer, therefore less to go wrong in the cluster program itself) and faster recovery are usually sufficient to recommend the resource driven approach over the quorate approach for a modern cluster..

Some clustering approaches try to gain the best of both worlds by attaching quorum resources to every hierarchy in the cluster.