Be Careful of the 9th Host in the Cluster

I was looking yesterday at post from Matt McSpirit regarding the Cluster Limits of Hyper-V. I started to look at how this would compare to vSphere.

I do not want to go into who can cram more VM's into a cluster VMware / Hyper-V? I did notice something that I realized - I think I should point out.

Take the following Scenario.


Now you want to add another Host to your cluster.

On pg. 7 of The Configuration Maximums for vSphere 4.0 and vSphere 4.0 Update 1 you will see that when adding the 9th host - the number of VM's per host is limited to 40.

So therefore the scenario will change to this:


In thinking that you can increase your capacity in your Cluster but adding another host - you just reduced the number of VM's that can run in your cluster 280!! In order to get back to the same amount of VM's you were previously running - will need another 7 additional hosts

As always my advice is - read the documentation and research the implications of your actions will be.