A recent discussion came up where a forum member has a setup of older hosts in one cluster and a set of newer hosts in another cluster
The question was should they combine the cluster or should they leave it as a set of smaller clusters.
Questions to ask:
How many hosts are we dealing with?
The maximum in a cluster is 32 hosts (see here )
If the number is above or close to 32, maybe you are better of distributing them.
If we are dealing with 4-5 hosts, its better to keep them together
How different are the hosts' hardware?
Are there significant cpu enhancements on the newer hosts that your vms will take advantage of?
Then use different clusters
Are the hosts different cpu types? Intel and AMD?
Then of course, use different clusters
Are the cpu enhancements not important?
Then you might want to keep them together
How is HA configured?
Is admission control policy based upon host failures or percentage of cluster resources?
A larger cluster can tolerate hosts failures better
Wha are the distances between the hosts?
If the hosts are in the same datacenter one cluster is better.
Are they spread out over different buildings or distance. Depends on latency and requirements.
If one set of hosts is in NY and the other is in Virginia then it makes sense to use different clusters.
If the hosts are in a wan with low latency, it depends on bandwith ,etc
Is DRS enabled?
A larger cluster can distribute load across more hosts.
When entering maintenance mode, more hosts mean more resources for downtime.
The answer really depends on your needs and limitations that you have to work with.
I prefer larger clusters for their ability to handle faults better due to larger numbers
Duncan Epping is also on that track
"Typically, I feel that most environments would benefit from 1 large cluster... if you compare it to the benefit they would have from not using EVC I think it is neglectable. go big!"
Pasted from <http://communities.vmware.com/message/2117798#2117798>
here is a article by Duncan on the topic : http://www.yellow-bricks.com/2012/04/10/cluster-sizes-vsphere-5-style/
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