Hyperthreading *NOT* Reccomended with Virtual Server 2005
Virtual Server 2005 supports multi-processor hosts (including those with hyperthreading) just fine – although, the guest OSes will never see more than one processor. The host operating system and VS2005 will “do the right thing” and try to distribute requests across the processors it has available to it.
However, in high load situations, hyperthreading can actually cause the performance of the host and VS2005 to degrade. This isn’t specific to VS2005 – it’s a more widespread HT problem found in many different scenarios. Best practice reccomendation for hyperthreading and VS2005 is to disable it – preventing you from getting into a situation where your performance is being degraded do to additional user requests, disk I/O, etc.
