Facebook uses 10,000 Blu-ray Discs to create petabytes of “cold storage”

Facebook has built a prototype cold storage system that uses Blu-ray Discs instead of traditional drives.

"The Blu-ray system reduces costs by 50 percent and energy use by 80 percent compared with its current cold-storage system, which uses hard disk drives," the IDG News Service reported, based on a talk given by Facebook VP of infrastructure engineering Jay Parikh at yesterday's Open Compute Summit.

The prototype storage cabinet reportedly holds 10,000 Blu-ray Discs for a petabyte of data. The idea is to store rarely accessed files, such as backups of users' photos and videos, and not the primary copies that need to be on faster storage systems so they can be accessed immediately.

Facebook expects to eventually increase the capacity of each cabinet to 5 petabytes. 

The design of the Blu-ray system will likely be made public through the Open Compute Project, which Facebook created to share hardware designs. IDG reports:

Parikh showed the system on stage at the Open Compute summit. Outside it looks like a plain server cabinet, about 7 feet tall, but inside there's all kinds of robotic wizardry to move the discs around.

The discs are stacked in piles, and a robotic picker can quickly select a disc from a pile and move it to one of 16 burners in the system, which write data to the discs.

Facebook is still deciding which parts of the design it will submit to Open Compute Project, Taylor said.

The prototype would have to be using 100GB Blu-ray Discs to hold a petabyte on 10,000 discs. The more common and much cheaper 50GB Blu-Ray Discs would seem to be more cost-effective based on consumer prices, but Facebook obviously buys through different channels. We've asked Facebook for more information and will provide an update if we get one.

Separately, Facebook said last year that it's considering the use of flash for cold storage. That would seem counterintuitive, but Facebook's idea is to use "the worst flash possible" to reduce costs, knowing that quality is less of a concern because cold storage devices don't need to be written over many times.