Designing Scalable XenDesktop Farms Q&A

Paul Wilson, architect working in the Citrix Worlwide Consulting Solutions team, hosted a webinar “Designing Scalable XenDesktop Farms” on 22 September. This webinar is still available on Citrix TV.

Based on this webinar he created a blog post giving answers to the questions he wasn’t able to answer at that time.

Here is a snippet from that blogpost:

“…Q: Are there any differences in scalability between hypervisors (Hyper-V, ESX, XS)?

A: This is a very common question. I wish I could give you a clear, straight-forward answer. Generally speaking, the hypervisor with highest desktop density would be considered the most scalable. In projects where I have been involved in running the same workload on the same hardware and varying only the hypervisor, the variance between the top and bottom performer is less than 10%. In other words the top performer might support 85 desktops while the worst performer only 80. Furthermore, I have seen results where each of the three hypervisors supported by XenDesktop have been rated at the top, therefore I must conclude the most scalable hypervisor is tied more closely to the workload and operating system than to the hypervisor itself.

To answer the question more directly, I would say at this time they do have slight difference depending on the environment they are used in. I also believe that as the vendors continue to focus on increasing density and as hypervisors become more of a commodity that this variance will continue to decline

Q: Will there be a possibility to provide more cores/threads for client OS using XenServer? I know this is more a XenServer than XenDesktop question, but XenServer shows all threads as CPUs and there is CPU-limitation in Win7.

A: I had to reach out to product management in order to get you an answer to this question. It turns out that XenServer (versions 4.1 and later) supports this with Intel chips. Basically you set a parameter to assign multiple cores to a socket. For instance, you can set four cores per socket and then assign eight cores to the VM to essentially give the VM 2 CPUS with multiple threads…”