Two metrics are emerging as industry standards for measuring data center power consumption: Power Usage Effectiveness and Data Center Infrastructure Efficiency.

Both metrics are backed by The Green Grid, an industry consortium formed last year to develop standards for measuring data center efficiency and productivity (see "Where to turn for advice about power"). These metrics are used to compare the amount of electricity the data center consumes for power and cooling with the amount of power used by the data center's IT equipment.

"Site infrastructure overhead is a simple concept," says Ken Brill, founder and executive director of the Uptime Institute, which provides consulting services to more than 100 data center operators. "It's easy to measure and captures everything."

Here's how The Green Grid defines these two metrics for measuring data center infrastructure overhead:

1. PUE = Total facility power IT equipment power PUE is a ratio. Should be less than 2; the closer to 1, the better.

2. DCiE = IT equipment power x 100 Total facility power DCiE is a percentage. The bigger the number, the better.

"The word about these metrics is really getting out into the community," says John Pflueger, technology strategist at Dell and a member of The Green Grid's Technical Committee. "These metrics have been discussed in some of our meetings in Europe. Policymakers at the U.S. Environmental Protection Agency and the Department of Energy are very aware of these metrics."

A lot of work remains, however, to document ways to collect power-consumption data and to apply these metrics so they can be used to compare the efficiency of data centers in different organizations, Pflueger says.

This year, The Green Grid will be working on productivity metrics. In particular, the group is interested in measuring the useful work coming out of a data center.

"This is something that people have been looking at in our industry for a while. It's a hard problem," Pflueger says. "One of the reasons why this is such a hard problem is that what counts for useful work at an [Advanced Micro Devices] data center might not be the same thing as useful work in a Dell data center."

The Green Grid ultimately hopes to come up with a metric - like miles per gallon for automobiles - for data centers.