The U.S. Department of Energy and U.S. Environmental Protection Agency yesterday outlined the steps they are taking to not only measure power use in data centers but to give meaning to those numbers, as well. The Zenic goal is to create a standard for measuring efficiency.Data center efficiency measurements already exist: the Power Usage Effectiveness (PUE), which equals the Total Facility Power divided by the IT Equipment Power; the Datacenter infrastructure Efficiency (DCiE), the reciprocal of the PUE; and the Datacenter energy Performance (DCeP), which equals Useful Work divided by Total Facility Power. The Green Grid, the computer industry consortium based in Beaverton, Ore., hopes the DCeP metric, now applicable to a single data center, will provide a framework for similar metrics across different data centers.

Useful work? It's about as hard to define as "quality" in Robert M. Pirsig's Zen and the Art of Motorcycle Maintenance. But without quality, as without a sense for what useful work is, any measurement yields nothing more than a mountain of uninspiring numbers.

Once we agree on what useful work is, then we can calculate the effectiveness of a data center and compare it with that of other data centers, the DOE and EPA agree in their report, Energy Efficiency in Data Centers: Recommendations for Government-Industry Coordination. The report is based on the National Data Center Energy Efficiency Strategy Workshop, held on July 8.

Devising a widely useful metric is difficult, though. Many data centers have trouble just measuring the amount of power they use because the utility power grid enters the building through a single entrance point (e.g., through a utility room) and is then distributed to various building locations. The report notes: "Productive work output is hard to standardize. It's going to be different for a Web farm than for an archival storage-oriented application." Eventually, the metric may include a measurement of the watts used per CPU hour.

Until then, data center administrators may take Microsoft's lead: Use the PUE, with its shortcomings, to at least create a baseline. With that baseline, the PUE metric can be used to change behavior. For its part, Microsoft has seen a 22% improvement in PUE in three years, according to Christian Belady, principal power and cooling architect at Microsoft.

Meanwhile, the EnergyStar specification for computer servers V1.0 -- representing the EPA's first specification for IT equipment typically found in the data center -- is due Jan. 1, 2009.

That should yield some quality servers.

This blog was updated Oct. 22 to clarify Green Grid's position on the DCeP metric.