As photo uploads accumulate on Facebooks data center servers, a new facility was built to store the old data

by: JASON CHANEY - Facebook data center site director Chuck Goolsbee displays a collection of four terabyte drives used in the cold data storage server racks.

To fully understand the need for cold data storage at the Prineville Facebook Data Center, it helps to draw an analogy.

Think of uploading photos to Facebook as users tossing printed pictures on a table for others to view. At the time, those pictures see plenty of action on the social networking site.

“When somebody uploads a photo, everybody is looking at it, commenting on it, ‘liking’ it, and sharing it,” said data center site director Chuck Goolsbee.

However, after time passes and the newness wears off, new photos are thrown on top of the pile, and before long, the older ones at the bottom rarely — if ever — get any attention.

As all of the photos pile up, it creates a greater demand on the web servers that Facebook users rely on each time they visit the site. That, in turn, creates a greater power draw for a facility that tries to use as little electricity as possible.

According to Michael Kirkland, the communications director for Facebook's infrastructure and engineering groups, the social network's 1.15 billion users have already uploaded about 250 billion photos and they continue to add another 350 million more photos per day.

Consequently, this past January, data center staff began work on a concept known as cold data storage. To continue the printed-photo analogy further, the data center sought to create the equivalent of a book shelf full of empty photo albums that they would fill with pictures as they are relegated to the bottom of the pile.

To that end, PRN 4, a building dedicated solely to cold storage was completed in July. Unlike the two approximately 150,000 square-foot data center buildings that house the servers that support daily use, the cold storage facility consists of a "spine" that supports up to three "shed" extensions where the cold data storage servers reside. At full build-out, facility provides about 64,000 square feet of space, but so far, only one shed out of three has been built.

“It is designed for just one thing — storage of data over a long period of time,” Goolsbee said. “It’s a very stripped down, very basic data center.”

Facebook has only recently begun to utilize the new facility. Goolsbee said they began to transfer data last Thursday. As a result, the server racks occupy a small portion of the building, and the rest remains vacant awaiting future use. Unlike the main data center facilities, where all the server racks were installed before going live, the cold storage servers will only be added as needed.

Each rack is capable of storing four petabytes (approximately 1 million gigabytes) of data, so Goolsbee estimates that the first shed will provide them the space to add new cold storage server racks until about 2017. Once they fill that shed, they can add a second or third one as needed.

Whether they will need to build more cold storage facilities remains unknown at this time, although Kirkland said the need for it will only continue to grow as more people utilize new digital technology. He has seen estimates that by 2020, there will be 40 zettabytes (approximately 40 trillion gigabytes) of data in the world.

“This is Facebook’s solution to it,” Kirkland said.

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