The Latest on Power Usage Effectiveness (PUE)

Written by Rakesh Dogra

The technical language related to any field including IT is full of acronyms most of which are quite handy. For many of us in the data center world we are now aware of the latest acronym; PUE. If you don’t let me tell you that it stands for Power Usage Effectiveness. In this article we will discuss about this term and the latest buzz in the PUE arena.

Data centers are energy hungry monsters and their need for energy keeps rising continuously. It reminds of a mythical monster in the Oriental philosophy that was named Sursa whose mouth increased in size in proportion to the prey that had to be devoured.

Attempts are being made to tame the data center monster so that they perform to their maximum possible ability while consuming the least possible amount of power by having the maximum possible energy efficiency. But then there needs to be certain parameters which define the efficiency and give a standard way to measure it.

The Green Grid which is a non-profit organization of IT professionals came out with two metrics known as PUE and DCiE which are mathematically reciprocal of each other, though the former has got a wider acceptance in the industry.

Mathematically the Power Usage Effectiveness is defined as the ratio of the total power consumed by the data center to the power consumed by the IT equipment.

PUE basically gives you an idea about the total power being consumed and the amount going towards actual computing purposes. The total power includes the power supplied to cooling equipment, chillers, lighting, storage nodes etc in addition to the IT power which counts the power delivered for servers, workstations, switches and so forth that are directly involved in the information processing going on in the data center.

This means that the PUE of an ideal data center would be one while on the upper limit it could go anywhere upto infinity. Of course the value of 1 is just a utopian idea and I don’t think there will be every a data center with such a value at least not with the current technology.

Regarding the actual value of PUE in the industry leading companies such as Google and Microsoft which have some of the largest data centers are really very efficient. A recent report published by Google stated that the efficiency of their data centers is in the region of 1.21 while Microsoft also expects their new data centers to have a value in the similar range of about 1.22.
However not all enterprise data centers have that value of PUE but lie somewhere in the region of 2.0. This effectively means that for every one unit of power which goes into their servers and other IT equipment, one extra unit of power is required for other purposes such as cooling equipment. A data center with a value of PUE above 3.0 is considered really poor in terms of its energy efficiency.

The increasing attention being given to data centers by the new US President may push the PUE metric forward. If the recommendation provided by IBM’s CEO comes to fruition then we will see Federal data centers more efficient in 3 years. To achieve this goal will require a measurement that may include PUE or some other metric. If a energy efficient measurement is adopted in Federal data centers it may not be long before it is adopted in data center throughout the US.

Reports and surveys have indicated that IT departments are less concerned about the energy efficiency of their facility and more concerned on the immediate cost savings. This frame of mind will need to change if energy efficiency in the data center is to have traction. It just may require penalties in the form of a tax from the Federal government or utility companies to change the attitude toward energy efficiency.

The adoption of such standards and metrics will also encourage manufacturers of IT equipment to produce more energy efficient products. The requirement will expand to other equipment such as mechanical and electrical systems and so forth.

Lastly it can be said that despite the slow adoption, PUE has become one of the most talked about metrics in the data center industry. For PUE to take shape as a green standard for measuring energy efficiency will require the convincing or pushing of CIO’s and the remainder of the C suite.

The true problem with PUE is not everyone is convinced that it is the most accurate measurement for energy efficiency in the data center. In addition, many believe that most data centers do not have the capability to properly measure and document such information.

At the moment the Federal government has not made any announcements regarding a mandate to make Federal data centers energy efficient. It is likely because Federal agencies like the Environmental Protection Agency, Department of Energy and research groups they sponsor have not come to a clear consensus on how to properly measure energy efficiency.

Other measurements such as Site infrastructure energy efficiency ratio (SI-EER) as defined by The Uptime Institute is essentially the same metric as PUE.

Measuring data center energy efficiency will grow in importance as energy costs escalate and the demand for powering IT equipment pushes the data center envelope.

Despite the lack of adoption, many including the originators of the Green Grid’s metric have been encouraging IT departments to monitor and document your data centers power and IT trends. The information may not provide an immediate insight, but it will give you a head start on tracking your data center against a mature metric along with provide a fingerprint of your data center energy consumption all of which most never had before.