Technology Lab / Information Technology


Cheap storage with a 50-year life span? Facebook spreads the gospel of Blu-ray.

Inside Facebook's Blu-ray storage rack.





Facebook VP Jay Parikh discusses cold storage and Blu-rays.

Facebook intends to use Blu-rays for "cold storage," data that can't be thrown out but may not be accessed for many years, if at all. The best near-term use case is backups of photos and videos, but the discs could also be used for any data that Facebook is required by law to retain for a certain number of years.

Facebook's cold storage today is entirely on spinning disks. The prototype Blu-ray system is estimated to be 50 percent cheaper than the disk-based cold storage, and 80 percent more energy efficient.

The discs are housed in a fancy rack that holds 24 magazines, with each magazine holding 36 cartridges, and each cartridge holding 12 Blu-ray discs, for a total of 10,368. A robot lives and works inside the rack.

"We have a robotic picker that will go to a specified magazine and then locate a cartridge, it will unlock that cartridge, removing the drawer, and a picker will go down and is able to select a specified disc in that 12-disc arrangement," Facebook's Giovanni Coglitore said in a video demo posted yesterday.

When the robot isn't working, the rack consumes virtually no power, he said.


Facebook is careful in how it's rolling out the optical storage system to production.

As Facebook does with other new technologies, "we'll start it out in what we call shadow testing," Frankovsky said. "Until it's proven, we'll take relatively small quantities, and we'll just mirror data from what's in production and shadow that data to the optical rack."

While Blu-ray can't match the performance of hard disk drives, that isn't as important for cold storage. Frankovsky also said the Blu-ray system will be "far superior to tape" because of its durability and performance.

It could also provide benefits in recovery from failure. Frankovsky said Facebook uses erasure encoding, which "distributes a file across multiple physical devices so that in any event of a failure of a physical device you can always recreate the file."

With disk drives, "you need to have a relatively aggressive erasure encoding environment where you have a lot more physical spinning disks, so you can sustain multiple failures and be able to recreate the file in any situation," Frankovsky said. Because the predictive annual failure rate for optical discs is lower, "it's quite possible that you won't need to over-provision how much optical capacity you have to be able to get the same level of protection with the complete file rebuild. There's kind of a double goodness there. Bit for bit, it's lower cost, and if we can over-provision less with optical, you can move that needle even further on the cost-saving side."

Separately, Facebook has also considered the use of substandard flash memory for cold storage. The idea is to take "partially good NAND flash which otherwise would have been sold off as thumb drives or potentially even scrap," Frankovsky said.

Flash storage is often thrown out by manufacturers when just a few cells have gone bad, he said. With smart enough software algorithms, "you can be cognizant of where the weak or bad cells are and write around those cells."

The bad flash initiative isn't as far along as the Blu-ray project. But both have progressed pretty quickly since Facebook revealed their existence last year, Frankovsky said. They could end up being important tools as data storage needs grow.

IDC predicts that by 2020 the entire "digital universe" will grow to 40,000 exabytes, or 40 trillion gigabytes.

"A large portion of that is going to be warm to cold data, and we need something better than tape and disk to store it," Frankovsky said.

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