Ruben Spruijt and Jeroen van de Kamp have just launched Project Virtual Reality Check (VRC), and I encourage you to stop by their site and view the first round of published white papers.

Here are the project’s objectives, as stated on the project’s site:

The goal of Project VRC is to investigate, validate and give answers to the following questions:

• How does various Microsoft Windows Client OS’s  scale as a virtual desktop?
• How does a VDI infrastructure scale in comparison (virtualized) Terminal Server?
• Which performance optimization on the host and guest virtualization level can be configured, and what is the impact of these settings on user density?
• With the introduction of the latest hypervisor technologies, can we now recommend running large scale TS/CTX workloads on a virtualization platform?
• How do the two usage scenarios compare, that is Microsoft Terminal Server [TS] only, versus TS plus XenApp?
• How do x86 and x64 TS platforms compare in scalability on bare metal and virtualized environments?
• What is the best way to partition (memory and vCPU) the Virtual Machines the hypervisor host, to achieve the highest possible user density?

If you have plans to virtualize desktops or terminal servers, you will find the information invaluable. The authors have published thorough test data, tuning best practices, and recommended configurations for VMware ESX, Citrix XenServer, and Hyper-V environments. The results provide good information on expected consolidation densities for each platform.

For context, these papers are not vendor-sponsored. They are coming from guys who having been doing large-scale desktop, application, and presentation virtualization implementations for a very long time. In my opinion, the results represent the most comprehensive, vendor-neutral, published benchmarks to date.

If you have plans to virtualize desktops or terminal services this year, these white papers are required reading. It’s the end of our quarter and I’m buried in work this week, so I won’t be able to conduct a full review of the benchmarks until next week, but here are my initial thoughts.

For starters, hypervisors were benchmarked on an HP DL385R5 2-way server running AMD quad-core 2356 CPUs at 2.3GHZ. The server was filled with 32GB of RAM.

The virtual desktop VM density results underscore the importance of hypervisor features such as memory overcommit and page sharing. The ESX host (which supports memory overcommit and page sharing) topped out at 70 virtual desktops in one benchmark. It should be noted that with memory overcommit and page sharing disabled, the ESX host ran a maximum of 25 virtual desktops. In comparison, XenServer and Hyper-V could run 30 virtual desktops simultaneously. Neither XenServer nor Hyper-V support memory overcommit or page sharing today, so they were not able to reach a comparable density as the ESX host. Note that in all cases, VMs ran the XP OS and were assigned 1 vCPU and 1GB of RAM. The authors fairly noted that in the case of the 70 virtual desktops on ESX that “real world figures would probably be more conservative.” This is true, but suppose you reduce the density by 20%. You are still left with 56 VMs on the ESX host. Vendors can use all the marketing talk they want to refute the benefits of memory overcommit, but the numbers speak for themselves.

I plan to post my thoughts on the Terminal Services benchmark results later this week. In the interim, I’m going to check with Ruben to see if they enabled AMD’s RVI during the tests. The benchmark doesn’t mention it, but since the CPU supports the feature, and since RVI can provide substantial memory performance improvements for a number of multi-threaded applications, it would be good to see its impact on the benchmark results. XenServer 5.0 and ESX 3.5 U2 both support RVI. For example, you can enable RVI per ESX VM guest by setting the following configuration option in the guest’s .vmx configuration file: monitor.virtual_mmu = “hardware”.

The whitepapers are freely available to all registered users. Also, if you would like to ask Ruben or Jeroen about their work in person, I encourage you to attend their session at the upcoming Virtualization Congress.