Info Paper

Why has DCIE vanished from our data centre vernacular?

By: Bob Landstrom

Do you remember bell-bottom jeans, platform shoes or puka shell necklaces? I mean, of course, the first time we had bell-bottom jeans - not that silly three month period in the ‘90’s. I had some of those back then. They were ‘groovy’ and I was really ‘digging it’.

I don’t dress that way anymore (even though I might secretly wish I could) and I certainly don’t say those things. We don’t use those words any more. They’re fine words, but they’ve just fallen out of fashion out of style. We use different language now even though we’re talking about the same thing. We did use ‘cool’ back then as we use it now. ‘Cool’ survived but ‘groovy’ is no longer hip.

DCIE is an acronym for Data Centre Infrastructure Efficiency. It’s the kissing cousin of Power Usage Effectiveness (PUE). The difference between them is very simple: PUE is the ratio of total facility energy to the energy consumed by the IT equipment. It’s a number that must be greater than or equal to 1.0. So we can have PUE’s of 1.8, 1.4, and 1.2 for example. DCIE is simply the inverse of PUE, expressed as a percentage. Thus, DCIE is a value representing the energy efficiency of a data centre expressed as a percentage equal to or less than 100%. For example, we could have a DCIE of 55%, 71% or 83% respectively. They measure the same thing but say it two different ways.

Some would say that of the two terms, DCIE is at least more intuitive. At one point, both were commonly used and generally one or the other was preferred depending on the country. Some preferred to speak in terms of DCIE rather than PUE. The reason being that using a percentage meant that higher performance was represented by a higher number, and this made a lot of sense. This was easier for some than recognising that a PUE greater than 2.0 was poor, that something around 1.4 was pretty good and that reaching 1.2 or so is very hard to do. Almost like a regional dialect, some preferred to use the term PUE and others preferred DCIE.

These days though it’s hard to find anyone using the term DCIE, and PUE seems to have won the hearts and minds of the data centre community.

It’s been a long time now since I’ve heard anyone use the term ‘DCIE’. In fact, curiosity has caused me to even go looking for it. In the Data Centre Energy Practitioner (DCEP) classes that I teach I’ve been asking students which term they prefer to use. For some years now no one claims to include DCIE in their vocabulary. As a matter of fact, my most recent class included students that had never even heard of DCIE.

So why then is it that PUE is established in data centre vernacular while DCIE did not? PUE and DCIE are two technical terms that describe exactly the same thing - neither is easier to compute than the other and both are subject to the very same precautions for proper measurement. Neither of them is immune to misuse by aggressive marketing, and neither offers a way to validly compare energy performance between two separate facilities. They have the same advantages and the same pitfalls.

The Green Grid, with development of an “xUE” family of data centre energy efficiency metrics including Water Usage Effectiveness (WUE) and Carbon Usage Effectiveness (CUE), has created momentum around PUE which could be accountable for declining use of DCIE. It’s possible too that the parts of the world which initially favored DCIE language were coincidentally less active in energy efficiency tracking, so that by the time their focus on energy efficiency intensified, the dialect of PUE was essentially harmonised.

PUE is now solidly in the data centre vernacular and is the primary metric that we use when talking about energy efficiency. DCIE may have been hip back in the day, but the time may have come to lock it away with our old clothes in the attic closet.

“When I use a word, it means just what I choose it to mean.”
- Humpty Dumpty, Through The Looking Glass, Lewis Carroll

“An academic dialect is perfected when its terms are hard to understand and refer only to one another.”
- Mason Cooley