Update 1/3/2012: We have had a few reports of customers re-enabling SNP features and running into problems because hardware drivers on systems were very old. Please make sure to update your network-related drivers before re-enabling (or enabling) those features!
Over the years, there has been a lot of debate around features in Windows which are usually referred to as Microsoft Scalable Networking Pack (individual features are known as Receive Side Scaling (RSS) and Chimney/TCP Connection Offload/TOE), and the effect of having them enabled or disabled on our servers.
Taking the trip down the memory lane - while it is true that when the features were released in Windows 2003 SP2, there were some issues to work out (in both Microsoft and 3rd party code such as network drivers) - the situation has improved dramatically over the years, to the point where disabling them can have significant impact on the performance of your servers.
Here is an example:
The following screenshot shows one of CPUs being overly taxed while others are not sharing the load. This is quite typical on a server with busy networking connection and RSS feature turned off:
The following shows a bit better what happens when RSS is in fact enabled on the server. The point of enabling it is illustrated by the red circle. Note how a single processor was very busy with networking traffic while the rest were not nearly as busy, and what happens after RSS was enabled:
Now that I have your attention - I wanted to point you to an article that one of my counterparts from Windows team, Tod Edwards, has written recently - which goes in depth on what those features are, why you should enable them, how to do so and also - how to make sure that you are in a good place when you do. Please go here to read it:
Give Microsoft’s Scalable Networking Pack Another Look
(It should go without saying but: please make sure that your network card drivers are updated!)