Early reports of SLAT-enabled processors significantly increasing RDS session concurrency

Let me caveat my next statement by saying that I think Hyper-V is a great virtualisation platform that meets the needs of many customer environments… but… Hyper-V does lack some features that would allow it to stand tall alongside the market leading product (VMware ESX) and I was disappointed when the dynamic memory feature was pulled from the second release of Hyper-V.

As I wrote when discussing new features in the Windows Server 2008 R2 release candidate:

“I asked Microsoft’s Jeff Woolsey, Principle Group Program Manager for Hyper-V, what the problem was and he responded that memory overcommitment results in a significant performance hit if the memory is fully utilised and that even VMware (whose ESX hypervisor does have this functionality) advises against it’s use in production environments. I can see that it’s not a huge factor in server consolidation exercises, but for VDI scenarios (using the new RDS functionality), it could have made a significant difference in consolidation ratios.”

Well, it seems that there may be a silver lining to this cloud (or at least, a shiny metallic grey one) as Clive Watson highlighted the results from some testing with Remote Desktop Services (Microsoft’s VDI broker) running on Hyper-V and reported that:

“We conducted our testing using both non-SLAT and SLAT hardware and found that SLAT enabled processors increased the number of sessions by a factor of 1.6x to 2.5x compared to non-SLAT processors.”

Basically using an SLAT-enabled processor (Intel Nested Page Tables and AMD Enhanced Page Tables) in a server should make a big difference to the consolidation ratios achieved in a VDI scenario.

Of course, if SLAT allows improved performance, then other platforms will also benefit from it (although not necessarily to the same degree) but, if VDI really is a feasible technology solution (I have my doubts and consider it a “significant niche” solution), I’m sure Microsoft will come up with something for the third incarnation of Hyper-V.

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