From the Lab

Why Today’s Power Metrics Are All Wrong

It’s time to change the way we evaluate power density in our data centers. Traditionally, the industry has rated power capacity by measuring watts per square foot, but the old standards are far less meaningful today than they once were. With hardware virtualization and higher-performance processors, companies are cramming a lot more into their servers than they were five or 10 years ago, and that’s having a big impact on power draw.

In addition, companies are now more apt to need different power capacity levels for different types of application workloads. Peak power usage for a hosted email application is different from the peak usage patterns involved in running big-data processing. And that means that a single overall metric for power density in a data center is less valuable than a declared range of power capacity that can be customized in delivery for different customer needs.

AFCOM, the association for data center management, now measures data center density by looking at kilowatts per server rack rather than watts per square foot. In AFCOM’s classification scheme, a low-density data center is defined as offering up to 4 kW per rack; medium density is 5 kW to 8 kW; high density is 8 kW to 15 kW; and extreme density is more than 16 kW per rack average.

That’s a good start in redefining power density standards. However, KeystoneNAP also believes that a modular data center layout lends itself to a more sophisticated measurement system – one that allows for allocating different levels of power to different workloads. If a data center promotes a range of power options for different server clusters, companies benefit through greater power efficiency. Greater power efficiency also translates into significant cost savings.

In the KeystoneNAP facility, an individual KeyBlock module holds 22 server racks , while a double KeyBlock holds 44 racks. Depending on what a customer needs, we can deliver a power-per-rack rate to a single KeyBlock that ranges from roughly 4 kW to 20+ kW. That spectrum runs from the lower end of AFCOM’s density scale all the way up to the extreme level. Some customers will need less power, and some will need more. Some customers will need less power for one portion of their server footprint, but more power for another.

There’s no question that power demand is on the rise, but how we define power density in a data center should take into account more than just the total capacity available. It’s not just the total power supply that’s important; it’s how you use it.