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PUE tries for standardization as green IT metric

The way to energy efficiency is through metrics, experts say. Now if only everybody would agree on one and start using it.

Experts agree that, for now, Power Usage Effectiveness (PUE) is the most accurate way to measure the energy efficiency of a data center. The trick for proponents of the metric, however, is to get CIOs to use it.

PUE is calculated by dividing the total power usage of a data center by the power usage of IT equipment (compute, storage and network equipment as well as switches, monitors and workstations to control the data center).

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CIOs working that equation should ideally end up with a number somewhere around 1.6, though many now have a PUE of as much as 3.0, according to The Green Grid, a consortium of energy-conscious IT professionals. Perfect efficiency would be a reading of 1.0. The equation's reciprocal, known as Data Center Infrastructure Efficiency (DCiE), presents the reading as a percentage (as in, "My data center is 78% efficient.").

The idea of PUE is to provide a measuring stick for CIOs to use when attempting to determine if changes they've made to their operations have actually improved efficiency, said Christian Belady, a member of The Green Grid technical committee and principal power and cooling architect at Microsoft.

PUE, developed by Belady and others, has become the calling card of the still-young Green Grid organization. It debuted just more than a year ago and has since received wide industry support as a concept and recognition in a report from the federal Environmental Protection Agency (EPA).

But it has so far escaped broad adoption.

"We need to get a metric out there and have the industry start speaking the same language," Belady said. "One of the things that companies need to do is start measuring it."

Belady said he hopes successful case studies, to eventually be released as white papers by The Green Grid, will help the momentum of PUE adoption.

Measuring in the real world


While proponents of PUE believe data center efficiency can be measured, the EPA isn't convinced. An August 2007 EPA report determined that "most data centers" do not have the "advanced electric meters or other monitoring systems that accurately measure and report data centers' energy consumption and efficiency."

CIOs looking to outfit their operations for PUE measurement have a few places to look, though. Belady encourages anyone needing help to join The Green Grid and browse the organization's white papers. In San Francisco and surrounding areas, energy utility Pacific Gas and Electric Co. (PGE) has actually loaned metering equipment to IT managers to help with the measurement.

If we wait
for perfection,
no one's going to do anything for five years.

Christian Belady
technical committee memberThe Green Grid

Mark Bramfitt, principal program manager for the high-tech energy-efficiency team at PGE, said the metering, automatic monitoring and dashboard tools that could be used to measure PUE are relatively affordable, even for a smaller midmarket IT shop.

"To get them there I think they need to install some equipment to do it," Bramfitt said.

To see benefit from PUE, though, more IT departments will need to start measuring it, allowing real evaluation of what products and techniques will significantly improve efficiency in data centers. And a standard will have to be decided on.

"Although it is a difficult process, defining energy performance is a prerequisite for implementation of many government and efficiency policies and programs," the EPA noted in its report.

So even though PUE is the most widely recognized efficiency metric, there are others out there. Site infrastructure energy efficiency ratio (SI-EER) as defined by The Uptime Institute is essentially the same metric as PUE.

"Before significant progress can be made in benchmarking data centers, basic terminology … needs to be agreed upon by the various stakeholders, and additional details related to measurement protocols for the site infrastructure efficiency needs to be worked out," the EPA notes.

What measurement protocols have been developed is still to be determined. Belady said The Green Grid is working on that. In the meantime, he's trying to encourage CIOs and data center managers to try a sort of best-guess attempt at measuring PUE.

"If we wait for perfection, no one's going to do anything for five years," Belady said. If IT managers begin measuring, even if the measuring is imperfect, it follows that they will both attempt to improve energy efficiency and begin a dialogue with their colleagues in the industry about how to best measure PUE.

Translating an equation into energy savings

Standardizing and spreading the word on PUE has been a challenge for The Green Grid. And it is only the first step. If it can become established as the metric, the hope is that it can be used to both produce a more accurate metric and encourage energy-incentive programs from utilities like PGE.

Bramfitt said he needs something like PUE to help determine which data center products and improvements are truly energy efficient and then provide financial incentives for companies that adopt them.

"Manufacturers just can't stick up their hand and say 'This is an energy-efficient product,'" he said. "I need to know how efficient it is."

That isn't easy to figure out, he said. Measuring energy usage on servers and other data center equipment is not as easy as measuring, say, home refrigerators.

"Just like a car has miles per gallon city and highway, a server might have miles per gallon for Web hosting and database stuff or email servers," Bramfitt said. "They're all configured to do different tasks better."

"I can run an incentive program that says 'Hey, Mr. Customer of Ours. Buy an energy-efficient server and I will give you a rebate,'" he said. "The problem is no one knows what an energy-efficient server is."


Let us know what you think about the story; email: Zach Church, News Writer

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