% Disk Read Time + % Disk Write Time not equals to % Disk Time?

These article is an extract of “Top Six FAQs on Windows 2000 Disk Performance” by Mark Friedman who also is the author of “Windows 2000 Performance Guide” that explains why the sum of % Disk Read Time and % Disk Write Time is not equal to % Disk Time. Why do we have to explain this? There are times that in Controller and Analysis, your client/user may observed that the total of % Disk Read Time and % Disk Write Time is not 100% and may question this to you. Therefore, a good understanding behind this will give you a build a positive credential to your client/user.

Often when you add the % Disk Read Time and % Disk Write Time counters together, they do not add up to % Disk Time. Furthermore, the % Disk Time counters are capped in the System Monitor at 100 percent because it would be confusing to report disk utilization greater than 100 percent. This occurs because the % Disk Time counters do not actually measure disk utilization. The Explain text that implies that they do represent disk utilization is very misleading. Read the rest of this entry »