Wrapping Performance Testing Introduction: What to Monitor (Plus Learning Resources)

The following is an article from Jim Holmes about performance testing.

"In this final post of my performance testing series I’ll help you figure out where to start, then pass on a few resources I’ve found extremely helpful in my own efforts.
What do I Monitor?
Figuring out which metrics, measurements, and counters to monitor can be extremely daunting—there are hundreds of individual counters in Performance Monitor alone! In most cases you don’t need anywhere near the entire set of metrics. A few counters will give us all the information you generally need for starting your performance testing work.
Most performance testing gurus will tell you just a few items will get you started in good shape:
Processor utilization percentage
ASP.NET requests per second
SQL Server batch requests per second
Memory usage (total usage on the server, caching usage)
Disk IO usage
Network card IO
If you’re doing load testing you’ll likely be interested in errors per second and queued requests. Often times soak or endurance testing will look to counters associated with memory leaks and garbage collection too—these help you understand how your application holds up over a long period of stress. However, those are different scenarios. The few counters mentioned above will get you started in good shape.
Where Can I Learn More?
Microsoft’s “Performance Testing Guide for Web Applications” is somewhat older, but remains a tremendous resource for learning about performance testing. It’s an extensive, exhaustive discussion of everything around planning, setting up for, executing, and analyzing results from your performance testing. The guide is freely available on Codeplex.
Steve Smith of NimblePros in Kent, Ohio, has been extremely influential in my learning about performance testing. Steve’s been appointed by Microsoft as a Regional Director because of his technical expertise in many areas. He blogs extensively on many software topics and has great practical examples for performance testing. He also has an online commercial course offered through Pluralsight that’s well worth checking in to.
The website Performance Testing has a great number of references to performance testing information across the Web. The site lists blogs, articles, training material, and other highly helpful information.
Go! Get Started!
Spend some time planning out your performance testing effort. Make sure you work HARD to only change one variable at a time. Don’t get flooded with information; more often less information can be more helpful at the start.
Performance testing is a tremendous asset to your projects, and it can also be an extremely fun, interesting, and rewarding domain to work in."

An interesting article about performance testing.