When the IO administrator asks for Oracle's IO requirements, based on the Statspack report time period, you can confidently say Oracle's IO requirements were 5.59 IOPS. And if the IO administrator wants the breakdown by read and write operations, or even in megabytes per second, that can also be provided.

Capacity is the other aspect of utilization. As I mentioned earlier, capacity is the empty glass-it is how much a resource can hold, can provide, or is capable of. Like requirements, capacity can take on many forms. A specific database server with a specific configuration has the capability to provide a specific number of CPU cycles each second or a number of CPU seconds each second. An IO subsystem has a specific capacity that can be quantified in terms of IOPS or MB/s. It could also be further classified in terms of IO write capacity or IO read capability. But regardless of the details, capacity is what a resource can provide.

We have already touched on gathering capacity data in a number of areas of this book, so I will make this brief. The trick to quantifying capacity is defining both the unit of power and the time interval. For example, the time interval may be a single hour, and the unit of power may be 12 CPU cores. Combining the time interval and the power unit-12 CPU cores over a 1-hour period of time-we can say the database server can supply 720 minutes of CPU power over a 1-hour period (12 CPUs _ 60 minutes) or 43,200 seconds of CPU power over a 1-hour period (12 CPUs _ 60 minutes _ 60 seconds / 1 minute).