Price-per-Watt Measure

Achieving a state of green IT means setting a measurable goal of computation work performed per watt consumed. Finding performance price per watt is as much art as science. IT managers will have to play a significant role in determining how to measure workloads, especially for servers, desktops and laptops. This is especially true for servers that are used in a virtualized environment.

The Green Grid has published a useful paper titled "A Framework for Data Center Energy Productivity." The paper discusses the pros and cons of using CPU utilization as a measure of computing work per watt consumed. For IT managers, the most important aspect of this discussion is to ascertain, based on knowledge of the server application workload, what is the most useful metric for a server, and then to implement a measurement and reporting mechanism.

For network and storage equipment, the measurement of work per watt consumed is clearly related to capacity and bandwidth processed over a given period of time.

There is a battle brewing among network equipment vendors that is based in part on the greenness of their products. It is important for IT managers to test network equipment in a production environment to get accurate numbers of performance per watt.

While some vendors provide information on network equipment at various load levels, these tests are almost always performed using test loads for relatively short durations.

For example, in my tests of Cisco Systems' 4900M 10 Gigabit Ethernet data center switch, I gathered my performance statistics using steady workloads running in 5- or 10-minute durations. Measurements taken every few seconds over a day or, better yet, a week would yield much more accurate numbers for understanding long-term power use. (See eWEEK Labs' review of the Cisco 4900M.)