Every now and then someone calls in and complains about terrible performance. Often times, the tech handling the call will try to recover performance by killing CPU intensive processes or closing unused applications¹, especially those with large memory footprints². More often than not, though, the issue can be described as file contention, a condition where performance is “penalized” because the disk cannot keep up with file IO demand.

In the example here, an unexpected virus scan kicks off in the background (these are usually scheduled to run after hours), and examining the two most common aspects of system activity, processor and memory, the workstation is well within the envelop of what is considered acceptable and the technician is left scratching his head as he tries to gauge why the system is so slow even though memory usage is minimal and CPU usage averages about 15%. I advise him to start Performance Monitor (perfmon) and connect some remote performance counters, mainly disk counters like read and write time, but most importantly average and current disk queue length:
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