Friday, 3 May 2013

European data centres are less energy efficient than you might think

imageData centre solutions company Digital Realty has released the results of its latest annual survey of European data centres. The headline findings are that almost 90% of respondents are likely to expand their data centres in the next year or two, the main reasons being (in order of importance) the need for security, disaster recovery and power issues. While respondents reported that data centre planning revolves around the supply and reliability of power and its efficient use, it’s disappointing that the average reported Power Usage Effectiveness measure (PUE – the ratio of total data centre power to power used by the IT equipment) is above 2.5.

The web-based survey, conducted by Campos Research in January 2013, included 201 IT, Finance or Real Estate executives from companies with €500m/£500m revenue or 2,000+ employees. The survey was conducted in France, Germany, Spain, UK, Netherlands and Ireland (although more than half came from the UK and France).

The finding that the average PUE is 2.53 comes as a surprise, at least for me – in fact the previous Digital Realty survey showed an average PUE of 2.61 in Europe, so this is actually an improvement. Other interesting data in the survey, including:

  • UK companies are the most likely to expand in 2013, particularly compared with those in France and Germany.

  • Most (68%) want to expand capacity in their own countries.

  • Security and connectivity are the main considerations in choosing a data centre site.

There’s much more in the survey report, with similar studies from Digital Realty covering the US and other markets around the world.


clip_image001Review:  Based on previous estimates you might expect the average PUE to be lower. For instance, a report to the US Congress from the US EPA back in 2008 predicted better values than that by 2011, as shown in the table. Similarly, In 2010 Energy Star produced it’s assessment of PUE ratios that showed an average of 1.91.


And just last year a survey by the Uptime Institute found that the average global, self-reported PUE was between 1.8 and 1.89

I talked to Rob Bath, VP Engineering at Digital Realty to get some insight into the high PUEs. The survey covers large companies that you would have expected to be better placed, and motivated, to address energy efficiency issues in their data centre, but it seems that the size of the data centres may actually be a contributing factor to the high PUEs.

According to Bath, “For large chilled water systems, which are most commonly deployed in the companies surveyed, the PUE will always be substantially higher if the utilisation of the data centre is low. That’s much more pronounced if the IT growth is small in comparison to incremental cooling infrastructure building blocks added to the system”. In other words small increases in IT infrastructure use may create a bigger jump in cooling energy use, bringing down the PUE. Capacity planning is important in order to match infrastructure deployment with the data centre space, so the smaller the available increments of IT growth the better the data centre will be able to reflect the levels of utilisation that give a better PUE.

Bath pointed out that using a greener data centre is very much on the agenda of these large companies. Apart from the corporate governance issues, energy represents 30-40% of the cost of running a data centre so a significant part of the equation. But it does seem to me that there are some significant data centre planning issues to be addressed if PUEs are to improve.

But does it matter anyway? The PUE is a fairly crude assessment of how green a facility is – efficiency doesn’t actually reflect the impact on greenhouse gas emissions. The Green Grid, which came up with the PUE metric, now has a Carbon Usage Effectiveness (CUE) which more closely reflects the impact of a facility, reflecting the benefit of using renewable energy, for example.

The PUE lives on, though. Facebook recently started publishing real time PUE and WUE (Water Usage Effectiveness) information on the web for its data centres at Prineville and Forest City in the US. At the time of writing, Prineville is running at a PUE of 1.06 and Forest City at 1.08. That’s the sort of level that big corporations in Europe should be aiming for.

© The Green IT Review

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