I fully understand the following link recommends not to do it because of "planning and monitoring challenges", but somehow that just doesn't sit right with me as a justification for turning off a performance enhancement. http://technet.microsoft.com/en-us/library/dd346699.aspx If memory serves me right, turning on hyperthreading gives an additional 20-30% perfornance increase. We have it on with our full Exchange 2007 infrastructure now and see 0 issues. Does anyone have any real world scenarios where leaving hyperthreading turned on with Exchange 2010 has caused issues/performance degradation? If I can find some real world scenarios, then I would be inclined to turn it off, otherwise this just seems like potentially "scared of the unknown" advice.

Hi Hotfix, I would advise you to have a look of below link where very good coments are added by Brian. http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/f0786eaf-3bd0-4511-87c8-fffbbdd98417/ Anil

Thanks Anil, I had seen that post, but basically said the same thing. I was looking for someone to provide evidence that it actually caused harm/negative performance to Exchange 2010. I don't think there are any cases of this happening probably because it hasn't hurt anything. Anyone have any negative experience to speak of?

There's nothing there or in Brian's post saying it will cause problems, just that it makes it hard to spec out your CPU requirements. 20-30% is not a guaranteed figure, and it depends on the application.

I would spec out my CPU requirements in that I didn't have hyper-threading, and just consider it a mini-boost to performance that I would never count on. So essentially there is no evidence that it causes problems which was the initial question. I appreciate you both chiming in.