Data center facilities pro

Aug 15 2008   8:08PM GMT

Key points to consider in the evolution of the PUE data center metric

Matt Stansberry Matt Stansberry Profile: Matt Stansberry


Yesterday I blogged about the Uptime Institute’s criticisms of PUE, specifically that the Green Grid metrics whitepaper does not explicitly discuss the need to gather PUE data over time. Microsoft’s Christian Belady (one of the key developers of the PUE metric) responded with the following:

“Ken [Brill of The Uptime Institute] has some valid points, clearly there needs to be more clarity and refinement in the definition to make it a rock solid benchmark. PUE is a “living metric” that the industry and in particular the Green Grid is working. But with all of the issues that are in the process of being resolved, here are three basic facts:
1) All metrics can and will be gamed regardless of the crispness of their definition. Show me a metric and I can come up with a way to game it.
2) Companies that are measuring PUE are improving their PUE over time. So they are improving their efficiency
3) Companies that are not measuring, are likely not improving. So these companies will be at a competitive disadvantage.

Microsoft is a company that is measuring (since 2004) and improving our PUE benchmarking against ourselves. There is no reason any other company cannot do this. Comparison with other companies is useful but less important to us as long as we demonstrate continuous improvement in our PUE. We hope that the issues people have with PUE for external benchmarking will be cleaned up in time but we do not plan on waiting until then for continuous improvement in our own operations.”

Here are a few key points to consider in the ongoing evolution of PUE:

Gaming PUE is going to happen
A lot of data center providers have included PUE ratios in press releases lately, many of them incredibly low. Rich Miller at Data Center Knowledge says he’s seen it before. “That’s pretty much what happened with the Uptime Tier System, which set forth a four-tier rating system for data center reliability. Data centers began describing themselves as equivalent to ‘tier three-plus’ or even ‘tier five.'”

PUE will need to evolve into a dynamic quality control metric
Dave Ohara at GreenM3 has a great explanation of how data center pros should use PUE in a dynamic way. “What helped me to think of PUE as a dynamic number is to think of it as quality control metric. The quality of the electrical and mechanical systems and their operations over time are inputs into PUE. As load changes and servers will be turned off the variability of the power and cooling systems influence your PUE. So, PUE can now have a statistical range of operation given the conditions. This sounds familiar. It’s statistical process control.”

Standards and training needed on how and when to measure PUE
Data center managers getting started with a PUE measurement program need some guidance — where, when and how do you take the most meaningful measurements? Microsoft’s Mike Manos and Belady have put together an excellent PUE Strategy post on their blog, The Power of Software. This checklist takes PUE newbies from measuring by walking around with a clipboard to data center chargeback. The Uptime Institute’s Pitt Turner has a great webcast on how to measure PUE on UPS and PDU equipment. The next step will be to get everybody doing this in the same way — which is where ASHRAE TC 9.9 comes in. The organization supports PUE and announced plans to develop a publication that would standardize PUE measurement methodology in November 2007, but no word so far on the progress of that project.

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