PUE is Still Broken and I still use it

PUE is still broken and I still use it. For more on why PUE has definite flaws, see: PUE and Total Power Usage Efficiency. However, I still use it because it’s an easy to compute summary of data center efficiency. It can be gamed endlessly but it’s easy to compute and it does provide some value.

Improvements are underway in locking down of the most egregious abuses of PUE. Three were recently summarized in Technical Scribblings RE Harmonizing Global Metrics for Data Center Energy Efficiency. In this report from John Stanley, the following were presented:

· Total energy to include all forms of energy whether electric or otherwise (e.g. gas fired chiller must include chemical energy being employed). I like it but It’ll be a challenge to implement

· Total energy should include lighting, cooling, and all support infrastructure. We already knew this but its worth clairifying since it’s a common “fudge” employed by smaller operators

· PUE energy should be calculated using source energy. This is energy at the source prior to high voltage distribution losses and including all losses in energy production. For example, for gas plants, it’s the fuel energy used including heat losses and other inefficiencies. This one seems hard to compute with precision and I’m not sure how I could possibly figure out source energy where some power is base load power and some is from peak plants and some is from out of state purchases. This recommendation seems a bit weird.

As with my recommendations in PUE and Total Power Usage Efficiency, these proposed changes add complexity while increasing precision. Mostly I think the increased complexity is warranted although the last, computing source energy, looks hard to do and I don’t fully buy that the complexity is justified.

It’s a good short read: Technical Scribblings RE Harmonizing Global Metrics for Data Center Energy Efficiency. Thanks to Vijay Rao of AMD for sending this one my way.


James Hamilton

e: jrh@mvdirona.com

w: http://www.mvdirona.com

b: http://blog.mvdirona.com / http://perspectives.mvdirona.com

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