How power-efficient is your data center? Most likely, you wouldn't know where to begin to calculate that. But a metric proposed by the Green Grid, PUE (Power Usage Effectiveness), is on its way to becoming a standard way to measure data center power efficiency. So it's time to get to know it.

In theory, it's simple to measure a data center's PUE. Take the total amount of power coming into your data center (what the Green Grid calls Total Facility Power), then divide that by the total IT equipment power in the data center. The lower the number, the better, because it means that most of the electricity is actually being used by the actual IT equipment. In the ideal world, a data center would have a PUE of 1, although that's clearly not possible.

What exactly is IT equipment power? It's the total amount of electricity used by IT equipment, including servers and computers, network equipment, storage, monitors, and KVM equipment.

As for Total Facility Power, that includes the IT equipment power, plus all devices that support the IT equipment load, such as UPS, PDUs, batteries, cooling system components, data center lighting, and so on. That's why an ideal, and impossible, PUE would be 1 --- all electricity would power the IT equipment itself.

Most data centers aren't set up to measure PUE. That's because many data centers aren't even metered. To properly calculate the PUE, you need to measure electricity going into the data center, and a meter is the best way to do it.

The Green Grid says that many data centers have a PUE of 3.0 or more, but that a 1.6 PUE is an achievable number if best practices are used. There's a related metric of data center power efficiency, called the DCiE (Data Center Infrastructure Efficiency). I'll have more on that in a future blog.

For more details about PUE and DCiE, check out this excellent white paper from the Green Grid.