Japan Betters PUE at Data Centers

Although the power usage effectiveness (PUE) metric is not without its problems, it is the de facto standard for measuring energy efficiency in a data center. Japan’s Green IT Promotion Council  wants to improve on PUE with its own metric, data center performance per energy (DPPE). The council (GIPC) wants to make this metric the world standard by promoting it to other organizations, such as The Green Grid. GIPC even published a white paper on DPPE in February.
GIPC’s definition of DPPE is somewhat convoluted, defining submetrics first:

  • IT equipment utilization (ITEU)
  • IT equipment energy efficiency (ITEE)
  • PUE
  • Green energy coefficient (GEC)

Conceptually,

DPPE = (IT equipment utilization * total IT equipment ability) / (total DC power consumption – green energy used)

= IT equipment real use / total power consumption

More precisely,

DPPE = ITEU * ITEE * 1/PUE * 1/ (1-GEC)

= (IT equipment utilization * IT equipment ability)

/ (total power consumed – green power used)

So they are saying that DPPE is a ratio of the actual IT equipment’s ability (because some of its total ability may not be used all the time) against the dirty power consumed.

GIPC claims that they came up with this metric after interviewing many data center operators and related companies.

Let’s look at two other metrics considered as improvements to PUE: data center energy productivity (DCeP) and corporate average data center efficiency (CADE). First, DCeP, under consideration at The Green Grid, is similar (but not identical) in spirit to DPPE.

DCeP is defined as:

useful work produced / total power consumption

This is different from DPPE in two ways:

  1. DCeP does not take the type of power (dirty or clean) into consideration.
  2. DCeP considers the output that is really useful.

Although I understand that the consideration of clean vs. dirty power may make sense, in reality we are not even close to the use of clean power for data centers yet. Although it is not possible to have all the power supplied by clean (green) power, if a data center is fueled by clean power alone, this ratio becomes infinity. Any metric that has a potential to become infinity may not be appropriate.

As for the second point, DCeP takes the software aspect somewhat into consideration. DPPE seems to simply count MIPS for given computing, regardless of what is produced. In an extreme case, you can run meaningless software to keep a server occupied and produce useless results. But I think DPPE is using this as a proxy for the useful work, as in DCeP. In addition, defining useful work has been a problem. That is why several proxies have been proposed for DCeP.

CADE, on the other hand, was developed by McKinsey, in conjunction with Uptime Institute.

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Energy Efficient Cooling for Data Centers: A Close-Coupled Row Solution
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CADE is defined as:

CADE = facility efficiency (FE) * asset efficiency (AE) where

  • FE = facility energy efficiency * facility utilization
  • AE = IT energy efficiency * IT utilization

This also is somewhat similar, although not identical, to DPPE.

Like any metric, DPPE has its merits and demerits. The Green Grid and other organizations have their own metrics for improving PUE. If DPPE is promoted as the world standard for energy efficiency at data centers, GIPC needs to have open discussions with The Green Grid and others. Everyone has an opinion on energy efficiency metrics, and no single metric can express energy efficiency perfectly.

In my opinion, Japan has been following many of the U.S.-led initiatives and technologies to date. Whether or not DPPE is accepted as a world standard for data center energy efficiency, it is a good thing for Japan to express its view outside of Japan.

Zen Kishimoto

About Zen Kishimoto

Seasoned research and technology executive with various functional expertise, including roles in analyst, writer, CTO, VP Engineering, general management, sales, and marketing in diverse high-tech and cleantech industry segments, including software, mobile embedded systems, Web technologies, and networking. Current focus and expertise are in the area of the IT application to energy, such as smart grid, green IT, building/data center energy efficiency, and cloud computing.

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