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Re: [Linux-cluster] Optimal number of nodes?



On Feb 8, 2007, at 1:13 PM, David Teigland wrote:

On Thu, Feb 08, 2007 at 01:00:59PM -0700, Tarun Reddy wrote:
I'm currently testing a RHCS 4 cluster with 4 nodes. Is there any
benefit from actually reducing this number down to 3? Other
clustering systems I've used seem to prefer odd number of nodes and
was wondering if RHCS has that same preference....

The odd number of nodes (votes) relates to quorum which requires over half of the nodes (votes) to be present for any to operate. So, if you define
three nodes (each with 1 vote) in cluster.conf, you need two in the
cluster to run. If you define four nodes in cluster.conf, you need three in the cluster to run. Both configurations stop operating if two or more
nodes are down.

Dave


Thank you Dave, that explains a lot and yet so simple. :-)

Just another question. In my cage I actually have a fifth machine, also running RedHat 4 but purposed for usage outside of the cluster. Actually adding it to the cluster, but limiting services only to the four "real" nodes would actually significant improve the tolerance of my environment by allowing any two nodes to fail or be powered off, correct?

Tarun


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