This short series of articles describes how Microsoft uses Power Usage Effectiveness (PUE), an industry standard metric for the efficiency of a datacenter. Being able to measure and monitor the effective power consumption of a datacenter in terms of the computing power it contains provides a way to ensure that you make best use of resources while minimizing your environmental footprint. This first article introduces PUE and looks at the issues that it can help you to resolve.

Part 1—"What Color is your Datacenter?"

Imagine if a child were to draw a picture of your datacenter. Does it look green, or is it a glowing orange or even as black as night? Look at the individual pieces of equipment in your datacenter—are any of them green?

If you want the picture of your datacenter to look greener (more energy efficient), you could try upgrading items to more energy-efficient equivalents, as if they were pieces of a puzzle that can simply be replaced. This upgrade method is what many companies are using as a way to convince themselves that they are reducing energy costs. The problem is that, unless you look at the big picture and understand how the pieces fit together, you could end up being disappointed with the outcome.


Figure 1 - Seurat's Sunday Afternoon on the Island of La Grande Jatte
George Pierre Seurat/The Bridgeman Art Library/Getty Images

Figure 1 shows an example of how the painter Seurat demonstrated a scientific approach to painting called pointillism, where the artist uses combination of color dots to create an image that is harmonious and effective, while minimizing the number of colors used. This approach is analogous to management telling their datacenter team, “I want a good looking picture where everything works together and uses as few resources as possible.”

A simple idea needs a simple metric to work. In Seurat's paintings, it is a visual test. For a datacenter, it is an efficiency value—"Tell me what the energy overhead is to run the IT equipment". Microsoft has been using this approach as long as anyone can remember, and when industry groups like The Green Grid started promoting a metric for datacenter efficiency, Microsoft was an early supporter and contributor to the standard as they had years of experience with their own datacenter efficiency metrics.

Getting the Picture Right

The last thing you want to do when measuring efficiency is create a picture that requires the viewer to cross their eyes and squint to see the magic hidden content. Seurat had the luxury of 2 years and over 60 sketches to support his technique for painting static views. However, datacenters are dynamic entities with thousands of interactions. When Microsoft took occupation of a legacy facility, the datacenter team spent 2 years evaluating hundreds of possibilities to drive a 25% improvement in the power and cooling infrastructure energy efficiency.

One of the most effective metrics Microsoft has used to get the correct view of datacenter efficiency is Power Usage Effectiveness (PUE). PUE is the total facility power consumption divided by the IT equipment power, providing a ratio of the power and cooling overhead required to support a unit of IT load.


By using PUE, Microsoft now has a historical record of energy efficiency, and the facilities to measure the efficiency of power and cooling systems.

A datacenter is a complex system and it is hard to get a total overall view of its operation. Microsoft uses PUE to step back and see the big picture, and yet still keep in focus how it all fits together. Many teams find it is a problem to zoom in on a detail and debate its merits without losing context of how this affects the related systems. One Microsoft datacenter engineer explains the benefits of using PUE compared to just measuring the total energy cost like this:

"I was constantly bombarded with vendors offering ways for my datacenter to run more efficiently. I also would hear many testimonials (bragging) from other facility managers who claimed to have squeezed more efficiency out of their DC. Since most savings on power can be turned into additional capacity, any efficiency gained could not be measured by simply looking at the power bill for energy savings."

Without a metric like PUE, the engineer could not measure the datacenter efficiency to see if it had improved.

So, how do you approach energy efficiency in the datacenter? Do you go for the low hanging fruit? Some options are the use of hot and cold aisles, raising room temperatures, and installation of more efficient cooling systems. Can you integrate these options into a strategy rather than a random approach? If you go after the low hanging fruit without measuring the overall effect, how do you know you are not playing a datacenter game of “whack a mole” ( by temporarily conquering energy inefficiency in one area until another a problem pops up somewhere else?

Given the complexity of datacenter design and operation, energy efficiency changes must be closely monitored for efficacy and overall effect. As you play with the control knobs making changes to your datacenter, you need to see the results. PUE is your indicator of whether things actually got better or worse.

In addition, there are other less obvious benefits from measuring and monitoring your PUE. For example, it exposes an energy-based model where power and cooling infrastructure and energy costs are allocated accurately. You can use the numbers to provide accurate information for accounting department actions, such as charge backs. Inaccurate charge backs against IT costs will create unintended consequences as business units try to manage and minimize IT costs. Accurate reporting of energy use allows people to gauge the impact of their actions.

In the next article in this series, you will see in more detail why energy efficiency is vitally important in today's economic climate.


  • Mike Manos, General Manager Data Center Services
  • Christian Belady, P.E., Principal Power and Cooling Architect