In the past not many people considered to run Terminal Services or Citrix PS/XenApp on virtual machines. Because of the intense usage of CPU resources(many processes and context switches) performance was not good enough compared to running terminal services on physical hardware.
But recently this has changed. Employees of Dutch companies PQR and Login Consultants developed an independant benchmark tool to measure performance of SBC and VDI solutions on bare metal, Hyper-V, VMware and Citrix Xenserver. They found out that virtualizing Citrix and Terminal Server is perfectly possible. Best practises are to use at least two vCPU’s per virtual machine and to not overcommit the CPU. The execution of the benchmarks were done as project. The project has been named Project VRC. See the website for more info.
At November 17 Project VRC announced the results of Phase 2 of the project. In Phase 2 new hardware and new hypervizors were used. Hardware used was the G6 generation of HP servers using the Nehalem CPU. Also Hyper-V 2, vSphere 4 and XenServer 5.5 were used. The exact results will be publised in two or three weeks from now as by then the whitepapers are available and vendors are informed about the results.
As a general note: the maximum number of users on terminal services using the new Nehalem CPU and latest hypervizors has increased quite a lot!