Real-world virtualization benchmarking: the best server CPUs compared

Heavy Virtualization Benchmarking

All tests run on ESX 3.5 Update 4 (Build 153875), which has support for AMD's RVI. It also supports the Intel Xeon X55xx Nehalem but has no support yet for EPT.

Getting one score out of a virtualized machine is not straightforward: you cannot add up URL/s, transactions per second, and queries per second. If virtualized system A turns out twice as many web responses but fails to deliver half of the transactions machine B delivers, which one is the fastest? Luckily for us, Intel (vConsolidate) and VMware (VMmark) have already solved this problem. We use a very similar approach. First, we test each application on its native operating system with four physical cores. Those four physical cores belong to one Opteron Shanghai 8389 2.9GHz. This becomes our reference score.

We then divide the score of the first VM by the "native" score. In other words, divide the number of queries per second in the first OLAP VM by the number of queries that one Opteron 8389 2.9GHz gets when it is running the Nieuws.be OLAP Database.

So for example, the OLAP VM on the dual Opteron 8389 got a score of 85% of that of the same application running on one Opteron 8389. As you can see the web portal server only has 39% of the performance of a native machine. This does not mean that the hypervisor is inefficient, however. Don't forget that we gave each VM four virtual CPUs and that we have only eight physical CPUs. If the CPUs are perfectly isolated and there was no hypervisor, we would expect that each VM gets 2 physical CPUs or about 50% of our reference system. What you see is that OLAP VM and OLTP VM "steal" a bit of performance away from the web portal VMs.

Of course, the above table is not very user-friendly. To calculate one vApus Mark I score per physical server we take the geometric mean of all those percentages, and as we want to understand how much work the machine has done, we multiply it by 4. There is a reason why we take the geometric mean and not the arithmetic mean. The geometric mean penalizes systems that score well on one VM and very badly on another VM. Peaks and lows are not as desirable as a good steady increase in performance over all virtual machines, and the geometric mean expresses this. Let's look at the results.

After seeing so many VMmark scores, the result of vApus Mark I really surprised us. The Nehalem based Xeons are still the fastest servers, but do not crush the competition as we have witnessed in VMmark and VConsolidate. Just to refresh your memory, here's a quick comparison:

(*) Xeon X5570 results are measured on ESX 4.0; the others are on ESX 3.5.
(**) Xeon X5570 best score is 108% faster than Opteron at 2.7GHz. We have extrapolated the 2.7GHz scores to get the 2.9GHz ones.

Our first virtualization benchmark disagrees strongly with the perception that the large OEMs and recent press releases have created with the VMmark scores. "Xeon 54xx and anything older are hopelessly outdated virtualization platforms, and the Xeon X55xx make any other virtualization platform including the latest Opteron 'Shanghai' look silly". That is the impression you get when you quickly glance over the VMmark scores.

However, vApus Mark I tells you that you should not pull your older Xeons and newer Opterons out of your rack just yet if you are planning to continue to run your VMs on ESX 3.5. This does not mean that either vApus Mark I or VMmark is wrong, as they are very different benchmarks, and vApus Mark I was run exclusively on ESX 3.5 update 4 while some of the VMmark scores have been run on vSphere 4.0. What it does show us how important it is to have a second data point and a second independent "opinion". That said, the results are still weird. In vApus Mark I, Nehalem is no longer the ultimate, far superior virtualization platform; at the same time, the Shanghai Opteron does not run any circles around the Xeon 54xx. There is so much to discuss that a few lines will not do the job. Let's break things up a bit more.