Have Google watchers been overestimating the number of servers in the company's data center network? Recent guesstimates have placed Google's server count at more than 1 million. But new data on Google's energy use suggests that the company is probably running about 900,000 servers.

Google never says how many servers are running in its data centers. The new estimate is based on information the company shared with Stanford professor Jonathan Koomey, who has just released an updated report on data center energy usage.

Google's David Jacobowitz, a program manager on the Green Energy team, told Koomey that the electricity used by the company's data centers was less than 1% of 198.8 billion kWh - the estimated total global data center energy usage for 2010. That means that Google may be running its entire global data center network in an energy footprint of roughly 220 megawatts of power.

"Google’s data center electricity use is about 0.01% of total worldwide electricity use and less than 1 percent of global data center electricity use in 2010," Koomey writes, while cautioning that his numbers represent educated guesses extrapolated from the company's information. "This result is in part a function of the higher infrastructure efficiency of Google’s facilities compared to in-house data centers, which is consistent with efficiencies of other cloud computing installations, but it also reflects lower electricity use per server for Google’s highly optimized servers."

Low-Power Servers, High Efficiency Data Centers

Google's data centers are designed to take advantage of industry best practices in design and operations. The company has been a pioneer in running warmer facilities and designing chiller-less data centers that use less energy. At the server level, Google's custom servers feature a power supply that integrates a battery, allowing it to function as an uninterruptible power supply (UPS). The design shifts the UPS and battery backup functions from the data center into the server cabinet.

Google is preparing to manage much larger fleets of servers in the future. The company has designed a new storage and computation system called Spanner, which will seek to automate management of Google services across multiple data centers. That includes automated allocation of resources across “entire fleets of machines” - ranging from 1 million to 10 million machines.

In addition to not disclosing server counts, Google also doesn't release data on the electricity it uses or provisions for its data centers. Local reports have suggested that Google arranges power capacity of 50 megawatts and beyond for some of its largest data centers. If the company is actually running its infrastructure using just 220 megawatts of power, that would suggest that Google is provisioning power for significant future expansion at these sites.

Koomey's report, "Growth in Data Center Power Use 2005 to 2010,” was prepared for the New York Times, which summarizes the findings this morning.

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