Google Boasts Of ‘Real World’ PUE Data Centre Rating

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Google has boasted of lowering its PUE rating for its data centres, making them even more energy efficient

Google continues to develop the energy efficiency of its data centres, and has revealed that it has achieved a ‘real world’ PUE (Power Usage Effectiveness) rating of 1.14.

The admission came in a blog post by Google’s senior director of data center operations, Joe Kava. He began by highlighting the fact that Google constantly tracks its energy consumption and uses that data to make improvements to its infrastructure.

PUE Metric

“As a result, our data centres use 50 percent less energy than the typical data centre,” boasted Kava, who described how Google uses the PUE metric to measure and improve its performance.

Power Usage Effectiveness (PUE) is the de facto measurement when it comes to the efficiency of data centres. PUE is essentially a ratio, namely the total power used to run a data centre to the amount used to power the servers.

The closer the result is to one, the more efficient the data centre is, because more of the power entering the facility is actually getting to the servers. For example, if a data centre has a PUE of 2.0, it means that for every watt of energy that powers the servers, another watt powers the cooling, lighting and other systems.

Google’s Kava revealed in his blog posting that the company’s trailing 12-month average PUE for 2011 was 1.14, which is an improvement from 1.16 in 2010. “In other words, our data centres use only 14 percent additional power for all sources of overhead combined,” he wrote

Kavo also made a point to stress how Google’s PUE figures are based on ‘real world’ calculations and raw data, not design specs or best-case scenarios. Google said that its PUE calculations include not only the electricity used to power the servers and cooling systems, but it also incorporate the oil and natural gas that heat its offices. It also accounts for system inefficiencies like transformer, cable and UPS losses and generator parasitic energy draw.

“If we chose to use a simpler calculation – for instance, if we included only the data centre and the cooling equipment – we could report a PUE as low as 1.06 at our most efficient location,” Kava wrote. “But we want to be as comprehensive as possible in our measurements.”

Rival Claims

This point about the purity of Google’s PUE rating could be a little dig at Facebook and other data centre operators who publish ultra-low PUEs. Facebook said in 2010 for example that its Prineville, Oregon data centre has a PUE rating of 1.15, but more recently reportedly said that it has achieved a PUE rating of 1.07.

“Our numbers are based on actual production data taken from hundreds of meters installed throughout our data centres, not design specs or best-case scenarios,” Kava wrote. “One way to think of it is comparing a car manufacturer’s mileage estimates for a new model car to the car’s real-life miles per gallon. We’re measuring real-world mileage so we can improve real-world efficiency.”

Google also said that it has been publishing its PUE quarterly since 2008 – and remains the only company doing so.

“We’ve seen dramatic improvements in efficiency throughout the industry in recent years, but there’s still a lot we can do,” said Kava. “Sharing comprehensive measurement data and ideas for improvement can help us all move forward.”

PUE Outdated?

However, there is concern that the PUE metric, which was developed as far back as 2007, is a fairly crude metric and is no longer the best tool for measuring data centre efficiency. Indeed some are beginning to question its usefulness at all.

In 2010 for example Charles-Antoine Beyney, president of the Carinae Group and founder of the Tier IV data centre in Paris which was described as the first “sustainable” data centre in France, said that companies should stop scrambling for PUE and instead concentrate on extending the lifespan of their facilities.

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Author: Tom Jowitt
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