Data Backup Digest

Data centres usually store everything on hard disks, all stacked up and cooled to keep the heat down, but Facebook have experimented with a disc-based solution.

At the beginning of this year, at the Open Compute Project in California, Facebook showed a prototype for their data centre storage design that makes use of Blu-ray discs. The system was made up of 10000 discs and was capable of holding a terabyte of data.

Facebook designed the system to handle their cold storage. This refers to data that has to be stored but is rarely, if ever, accessed. The majority of photos accessed on Facebook are those that are published recently, thus older ones can be pushed to cold storage. Facebook also keeps duplicate copies for backup data and is also required to store certain things for legal compliance. This type of data would just be wasting space on often-accessed drives, thus cold storage is perfect for it.

Facebook claimed that the Blu-ray system cut energy use by 80 percent and costs by 50 percent when compared with their current hard disk system. The savings are vast and it’s clear why Facebook are keen to investigate further.

Blu-ray discs are cheaper to buy than hard disks and are easier to increase the storage density of. Although hard disks offer superior performance, this isn’t a big issue when it comes to cold storage. Discs are slowly becoming a less lucrative market, but this data centre prototype could see the market given a new lease of life.

“Economies of scale could take over really quickly, and [Blu-ray disc manufacturers] could start producing those discs for the Open Compute community at much lower cost than they do today because, believe it or not, this is one of those areas where really high-capacity Blu-ray discs are in relatively low demand on the consumer side and in relatively high demand on the data centre side,” said Frank Frankovsky, VP of hardware design and supply chain operations at Facebook.

The discs are housed in a rack that is controlled by a robot. This robot locates a magazine, then the cartridge within, then removes the drawer and can find the disc within the arrangement. The company say that when the robot isn’t doing any work the rack consumes barely any power.

Each Blu-ray disc is certified for 50 years of operation, but you can get some that are reliable for 1000 years. The media is separate to the drive, so you simply replace the drive and don’t have to replace the data.

Facebook is continuing to research how they can best store data while consuming minimal power. The largest expense from running data centres is the need to keep huge amounts of drive running in optimal conditions. Being able to cut down on this could save the firm a lot of money in the long run.

One avenue the Silicon Valley tech company are looking at is low power flash memory, but at the moment reliable flash memory is too expensive to make that a viable solution.