For virtualization, which is better more cores or faster CPU?

We are going to be running Virtual Server on a Windows Server 2003 and 6 - 10 virtual machines. For CPU, which is better if you have to trade off one for the other, faster CPU or more cores? For instance a fast 2 core or a slower 4 core. Of course I know that having fast 4 core would be better, but if you have to trade which do you trade speed or cores? Links with tests/comparisons would help along with opinions.
BMCKRobAsked:
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DChaffeyConnect With a Mentor Commented:
There's two parts to this answer:
Firstly, it's very similar to a physical environment - if your host needs to run fewer, more cpu intensive guests, you buy faster CPUs.  If you are wanting to parallelize or run a load of guests, get as many cores as is feasible.

Secondly, there's a nice simple finger in the wind to use when sizing a mid-range ESX server.
Take the number of cores in the box you are looking at, subtract 1 for overhead, and multiply the remainder by 5 (for number of 1vcpu server guests), 7 (for 1vcpu VDI guests) or 3 (for 2vcpu guests or busy servers). Also keep in mind that once you've got a working ESX environment, people wanting to put more servers on it come out of the walls at head-height...it might pay to have some extra capacity!
For Vmware server the numbers are different, in that they are smaller by a decent margin, but it still gives you an idea where you are going.
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tinhnhoCommented:
it depends on you want to go for AMD or Intel and what application you wan to run on.  At my work place, we prefer to have mysql on Opteron box than Intel box. For my opinion is more cores are better.
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Lee W, MVPTechnology and Business Process AdvisorCommented:
I would prefer more cores, because (depending on Virtualization technology used) you can limit the VM to use only x cores, thereby ensuring that one runaway VM doesn't take down ALL VMs (in terms of processor utilization).
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Paul SolovyovskySenior IT AdvisorCommented:
More cores is normally better, just make sure you have enough memory per core to cover what you need to do.  Since you're running Windows 2003 it's not an issue but in VMWare ESX it is licensed per CPU and not per core so the more cores the better since it may require less licensing.
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BMCKRobAuthor Commented:
DChaffey, that was very helpful, thanks for the info. Since we are running a lot of low intensity guests, the it is better for us for multiple cores.
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