It's anybody's guess as to how many servers are housed in any large data center, and big names like Amazon and Google never talk about how many are running in their data centers. Facebook (News - Alert) is equally tight lipped about this. Server information is privy to only the chosen few and these guys play it real close to their chest.
However, having said that, it doesn't cost to guess, certainly not if you do it the James Hamilton way. Based on certain energy usage information that was recently disclosed by Facebook, he arrived at an estimate and shared his calculations via his Perspectives blog.
Hamilton went about the job in a very precise and analytical way. He started off by using the figures of the total annual power draw for Facebook’s data centers –509 million kilowatt hours--and concluded that the average data center power usage was 58 megawatts of power.
Applying the published Power Usage Effectiveness (PUE) of 1.07, he arrived at the fact that the social network is delivering 54.27 megawatts to servers. Assuming the power usage of an efficient server to be about 300 watts per server, Hamilton surmised that there were about 180,000 servers at Facebook's data centers.
While this is the most detailed analysis of Facebook’s power usage, the 1.07 PUE used by Hamilton would be relevant only to company-built data centers and not the rest.
As most of the energy used is consumed by its leased facilities in northern Virginia and Silicon Valley, the PUE here was likely to be much higher than the number denoted by Hamilton and this would indicate a lower server count than the one arrived at.
Also, Facebook has not indicated the PUE for its third-party data center space, and many of its facilities don't have the full open compute design that is typical of Prineville. All these facts could alter the figures arrived at by Hamilton. Having said that, industry reports agree with Hamilton's viewpoint that Facebook's server count is growing by leaps and bounds.
Plans for another data center at Prineville are afoot, but details available are vague. A new permit for a 62,000 square foot facility may point to a small fourth facility on the Prineville site. This is assuming that Facebook's initial plans to build three server farms there actually materialize.
Server Technology (News - Alert), a provider of quality rackmount power distribution and monitoring solutions that help manage power capacity, reduce downtime and improve energy efficiency, offers a variety of PDU products that provide reliable power distribution and measure the current in network devices. Its basic PDUs provide reliable power distribution for all of the devices in the equipment cabinet, from 2kW-6kW per cabinet. Its metered PDUs have local LED input current monitoring and allow network engineers to utilize the PDUs’ True RMS Power Monitor to precisely measure the current (in amps) that network devices are drawing on the power circuit.
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Edited by Rachel Ramsey