Friday 30 March 2012

PUE = 1

Well, next week I'm off to the 451 HCTS summit at the Russell Hotel in London followed by an Concurrent Thinking event on the EU Code of Conduct for Data Centres. This has set me thinking this week about the real future for data centres. Many consultants in the field will talk about energy efficiency as being getting the PUE as close to 1 as possible and I note that there is an ongoing ratings battle between google and facebook about whose PUE is better, as if it mattered!
It doesn't, as we all know (don't we!) PUE is the ratio of the total energy into a facility divided by the amount of energy that is used by the compute function (if you don't know then visit the Green Grid website)
This is expressed as a single number 2, or 3 or 1.16 or whatever, but it is NOT a measure of energy efficiency or indeed energy usage, it is just a number, and if I wanted to get pedantic I'd say that PUE is variable, as it actually is, because it is dependent on two factors, the first being the external temperature of the facility, as this links directly into the way your cooling system operates, warm outside, controls set to 21degrees, chilling will take place, 5 degrees outside, controls set to 21, no chilling takes place, thus colder outside less energy being used in chilling. So external temperature will affect your PUE, as will what your IT is doing, take for example 3 pm on the last Saturday before Christmas in a retail environment, lots of electronic transactions flowing through your payment systems, linked into your logistics systems for re-ordering etc, and you have a large IT load, contrast with 2am on a Sunday in August, do you think it's going to be anywhere near the same? Of course not, its going to be less or more depending on how your IT is used to support the business and the outside temperature, so PUE is variable and that delta could be quite wide so it amuses me to see the marketing spin put on the PUE figures. Another factor is two completely different organisations using PUE to trade insults "my PUE is smaller than yours" etc when their facilites are NOT comparable, a small retail chain for instance that has say 200 shops compared to a large cloud type search engine with multiple locations, but with huge facilities, say 100,000sq ft plus. The PUE cannot be used to compare, in fact the Green Grid website makes this very clear indeed, so marketing people huh? what can you do, well start by not spinning the truth would be a good start.
Anyway, I digress, the purpose of this blog is to think about those facilites whose PUE =1, WOW! 1 meaning that ALL of the energy in to the facility is going directly (do not pass AHU's, UPS, CRAC's Chillers etc, go directly to) IT. What does this mean? well it means that your facility is going to be using full fresh air, as it comes in from the outside, maybe with a filter to block those nasty particulates that reside in the atmosphere, and that you haven't provided any UPS's, so you're going to be at the will of your electricity company, and most importantly that you've saved money, and lots of it, and you continue to save it for every year that facility is operation (over your peers that is).
The capex costs of NOT providing resilience is something that you are going to have to explain to your IT and finance directors, ultimately its down to your risk appetite, can you withstand the loss of your facilities for the amount of time your power is down, do you have adequate backup, is your network resilient enough to go off site to a cloud facility to provide continuity? Do you in fact need to have compute on site? why not stick it all in the cloud and let them worry about the resilience, then because you only have network and the odd non cloudable app in your onsite facility, and you can get rid of that nasty HVAC system, that costs you the same as your IT to run and maintain.
If we all move to the cloud for our compute, we only need network, but that puts us in jeopardy, as we are now dependent on other organisations to support the platform that supports your business, its all down to risk.
I'll be at the event next week, please come and talk to me if you're there, it'll be emotional....

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