Just as with CPU utilization, IO utilization can be calculated. However, because of the possibility of file system buffer caching and IO subsystem caching, our Oracle-focused utilization calculation is a worst-case scenario (no caching assumed), includes only the instances we sample data from, and does not include any non-Oracle-related IO. So, the worth of our calculation is limited (at best). The higher worth metric is Oracle's IO requirements, which we calculated in a previous section.

The IO team can use Oracle's IO requirements, apply whatever caching metric they wish, and also add any other IO-related metrics. While our utilization calculation has limited value, when comparing the theoretical worst-case utilization with the actual IO subsystem utilization, it will demonstrate the effectiveness of caching, changing IO subsystem capacity, and possibly various tuning efforts.

Suppose the IO administrator told you the IO subsystem has a capacity of 250 IOPS. Earlier, in the "Gathering IO Requirements" section, we calculated that, during the reporting interval, Oracle processes generate 5.59 IOPS. Once again, using the utilization formula, we have this calculation: