Tuesday, 7 October 2008

Google Data Centre Efficiency

Google believes it's operating the world's most efficient data centres. The claim is based on PUE (Power Usage Effectiveness) metrics from the Green Grid, which is the ratio of the total power used in the facility to the power used by the IT equipment.

The company quotes a report to the US Congress from the EPA (Environmental Protection Agency) which provided a set of efficiency improvement scenarios predicting future data center energy consumption and associated PUE values to 2011, as shown in the table.

According to Google, "the EPA predicted that 'state-of-the-art' data centers, employing exotic energy-efficient power and cooling technologies such as liquid cooling and combined heat-and-power energy generation solutions, could reach a PUE of 1.2".

Google claims that the PUE results from all of its six data centres with IT load of more than 5MW that have been in operation for six months or more have an average PUE of 1.21, although none used the sort of techniques that the EPA assumed necessary to reach these levels. Not only that, but one of the data centres had an annual PUE of 1.15 and had reached a quarterly PUE of 1.13. "We believe that each of these data centres is more efficient than any other comparable (i.e. real-world) data centre currently in operation". Apparently the data centres have all been built since 2005 and are in different climates.

This is impressive stuff, but I know there would be a lot of questions from many of the people I've met in the data centre industry as to how they've done it. There are more details in the paper about how the measurement was taken and calculated, but no insights into how the efficiency was achieved. I hope Google will share some of the secrets of its success, given the potential CO2 gains across the industry.

Footnote: In a previous post I ridiculed the idea that a data centre could have a PUE of less than 1.0 (which apparently has been claimed in the past). Whilst I'm sure any claims up to now have been based on a misunderstanding of the metric, the Google paper does point out that "A PUE <1 would be possible with on-site generation from waste heat, but currently this is commercially impractical to implement". I think 'commercially impractical' is putting it mildly.

© The Green IT Review

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