The Green Grid isn't seeking absolute accuracy. It's aiming for "almost."

The organization, which is backed by a wide swath of technology companies, issued a white paper today that seeks input on a new set of metrics that will give corporations and IT managers a better sense of how much of the power they pump into their datacenters goes toward useful, productive purposes.

The trick, though, is to make it somewhat easy to calculate. The organization started with Power Use Effectiveness (PUE) which is the total power going into a datacenter divided by the power consumed by IT equipment. A PUE of three would mean that only one-third of the power would be going to the servers andstoragedevices: The rest would be going to lights and air conditioners. That's approaching meatlocker-level cooling.

In January, Advanced Data Centers said it was constructing a data center for the Sacramento Municipal Utility District that will have a PUE of 1.1. Google claims a 1.21, but that's only as long as you don't count the cafeteria (see Advanced Data Centers Claims Super Efficiency). (You can also flip the PUE figures, putting IT power on top, to come up with Data Center Infrastructure Efficiency.)

PUE and DCIE, however, don't take into account different types of server loads, peak computing periods, and other factors. The organization subsequently came up with a metric called DCeP to measure effective power performance, but it's a little unwieldy to calculate off the top of your head.

The goal of the new metric "is to find a proxy for a difficult measurement but that still gives a good indication of useful work completed," the paper stated.

What are some of the criteria for the new metric? It's got to be somewhat easy to use and should also reflect reality. Ideally, data center managers would be able to swap it like mileage ratings on a car.

So far, some of the ideas being discussed are to rate a data center on a particular application, or sample workloads. Bits per kilowatt hour has also been suggested. Another one is to examine power through the lens of processor utilization. Also on the boards is "compute units per second."

While PUE and other ratings are voluntary, metrics like this can take on a life of their own. Energy Star ratings for servers, for instance, are purely voluntary. Because many government agencies are required to favor Energy Star equipment, however, it becomes a de facto standard, according to Subodh Bapat, who runs the energy efficiency efforts at Sun (see Is the Internet Carbon Negative? Yes, Says Sun).

Right now, the industry is working to amend the Energy Star server ratings because they rate servers on power consumption while the servers are idling. That makes as much sense as rating car mileage by what they burn at stoplights, he said. The industry wants to see ratings based on actual work performed.