I moved this question from StackOverflow because it makes more sense to have it here
We have decided to go with a virtualization solution for a few of our development servers. I have an idea of what the hardware specs would be like if we bought separate physical servers, but I have no idea how to consolidate that information into the specification for a generalized virtual server.
I know intuitively that the specs are not additive - I shouldn't just add up all the RAM requirements from each machine to get the RAM required for the virtual server. I can't really treat them as parallel systems either because no matter how good the virtualization software is, it can't abstract away two servers trying to peg the CPU at the same time.
So my question is - is there a standard method to estimating the hardware requirements for a virtualized system given hardware requirement estimations for the underlying virtual machines? Is there a +C constant for VMWare/MS Virtual Server overhead (and if so, what is C?)?