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Facebook looks to cold storage to minimize server costs.

No, I’m not talking about the icy fighting champion of 90’s video game fame. “Sub-Zero” is the unofficial name of the new data center that Facebook is building in Prineville, Oregon, according to their recent planning permits. Wired reports that the new facility will cover 62,000 square feet, and that this kind of data center has a unique purpose – it’s being designed to not be used much. Facebook will be unloading the billions of old and unused user photos to these servers, which will be kept turned off most of the time to save on power costs. The term for such a system has come to be known as cold storage, and may utilize a cloud or MAID (Massive Array of Idle Disks) structure.

To put things in perspective, Facebook had 140 billion pictures as of 2011, which is 10,000 times more raw data than the Library of Congress alone. Now consider that they receive 30 million new images per day, and that people worldwide take more photographs with every passing year. All of those files have to go somewhere, yet can’t just be put on hard disks and left in a closet because they need to be accessible. So the solution is to collect a huge amount of only-sometimes-running machines into one room. In a traditional data server environment, cooling and power concerns limit how many units you can have in one place. But when you’re planning to only ever be at twenty to thirty percent capacity at any given time, you can use more space for less money. Right now, a rack of Facebook servers consumes 4.5 kilowatts of power. They intend on Sub-Zero servers falling to 1.5 kW.

For users, this means that older photos may take a few more seconds to access while the sleeping disk spins up to speed. But ideally, commonly accessed photos (like profile and wall photos) will remain in the regular data centers, so users will probably never know the difference once Sub-Zero’s servers power up.