A: It depends.
No, seriously, as much as it sounds like a copout, that is actually the correct answer.
I still get asked this question several times a week. After a deep breath, I carefully say “it depends”, but then try and explain my position. Part of the problem comes from looking at virtualization as something you might do to a server, instead of looking at it as part of how you manage all your servers.
In the olden days, say four years ago, it was a pretty simple question in that the options were limited. Processors had a single core, and you had a choice – do I go with two processors or four. Four processor systems had more room for memory, but they also had more processors.
Today things are more flexible and more fluid, and this trend is only increasing. Processors have multiple cores, and the options are vast. Intel is introducing new processors into the Xeon family soon. The Nehalem EX and the Westmere EP. All of these benefit from the architectural advantages that came with the introduction of the Nehalem architecture. All of them have multiple cores. So how do we pick the right virtualization server – the “best” virtualization server?
There will be a lot of dials we can turn. A given server could have two, four, or eight processors. Each processor could have four, six, or eight cores. Different servers will have different memory capacities and I/O capabilities.
To make a good choice you will need to understand which resources constrain the addition of more VMs to your servers. Understanding your workload is the key.
As you load virtual machines onto your platform what barriers do you run into first – memory? CPU? Disk I/O? Network I/O? Something else?
Choosing the right server will require understanding your workload, and selecting the hardware that best addresses your virtualization constraints, without breaking your licensing or budget.
There is no magic answer – the right server for your VMs depends on what your VMs do. Are they web heads, sharepoint servers, data bases, or ERP modules? The right answer depends on understanding your workload. Or as I said before, It Depends…