You can find hardware recommendation for Test Agent / Test Controller here: http://msdn.microsoft.com/en-us/library/ms253092%28VS.90%29.aspx
But still people have some questions / confusions around it because of these reasons:
1)Above link talks about h/w requirements for VS2008 and there is no similar link available for VS 2010.
2) The number of virtual users that an test agent can generate will vary widely from test to test because of variance in think times, response size, response time etc. so people want to get more details here so that they can correlate it with their scenario and accordingly evaluate how much load they can generate using an test agent of a particular config.
Reason for #1 is that There was NO change in h/w requirement for Test Agent / Controller in VS2010 and it remains as of VS2008.
To address #2, We did some baselining runs using IBuySpy sample app. Our pages had average response size of ~32KB, avg response time of 3ms and avg think time used was 3secs. We kicked off multiple runs of different different durations on different config boxes and came up with these h/w recommendations for test agent box:
Number of vUsers
Avg RPS (Req / sec)
<1000 virtual users
Single Proc Dual Core 2.6GHz
We can scale up to 3000 or more vUsers on this config but it will cause dip in RPS. We've seen Avg RPS of 2000 at user load of 3000.
<2000 virtual users
Single Proc Quad Core 2.6GHz
We can scale up to 6000 or more vUsers on this config but it will cause dip in RPS. We've seen Avg RPS of 4000 at user load of 6000.
N x 1000 virtual users
Scale out to N agents each with Single Proc Dual Core 2.6GHz
Please note that the guidelines presented here are provided as general guidance for hardware planning. As mentioned above, Number of vUsers and RPS will vary from test to test depending upon many factors like think time, response size, response time etc.
Let me know in case of any Qs / issues. You can post your query here as well.