Facebook is looking for some really bad flash.
The social networking behemoth already relies heavily on NAND flash for many of its services, taking advantage of its high performance to quickly give users the latest from their friends. Now it wants to use a new type of flash for long-term storage of data such as photos and videos, which are hardly ever changed.
With the new technology, which Facebook calls “cold flash,” the company wants to take flash in the opposite direction from where most users and vendors are looking for it today.
Flash gives faster access to data and takes up less power and space than hard disk drives, but it tends to lose capacity over time as new data is written on it. Most flash storage vendors are working to make the media faster and increase its longevity. By contrast, cold flash would have low endurance and low performance, according to Jason Taylor, Facebook’s director of infrastructure. He spoke on Tuesday morning at Flash Memory Summit in Santa Clara, Calif.
“Make the worst flash possible,” Taylor asked a large audience of flash industry executives and engineers. Cold flash only needs to be dense and cheap, because it’s a WORM (write once, read many) medium, he said. Writing a bit of data to it could take 10 times as long as usual for flash, and it won’t need the capacity to be reliably written over many times.
With cold flash, Facebook would write data to it once and keep it around to be “read,” or viewed, over a long time. Most companies use hard disk drives for that kind of data today, at a much lower price per bit than flash commands. But by leaving out some of the qualities that developers have been trying to improve in flash, manufacturers could make it more cost-competitive with hard drives.
The types of Facebook data that would go into cold flash would be photos, videos and other content that tends to stay the same after it’s created. As for how many times those are likely to be read, Taylor offered no guarantee.
“The majority of that data will probably be written once and read never,” he said.
Facebook might also use cold flash for log data that it needs to keep for a long time and may analyze later, he said.
Asked whether the company had talked to flash vendors about manufacturing cold flash products, Taylor declined to comment.
Facebook uses just five types of servers in its production facilities, which allows the company to order gear at volume prices that is configured for its own needs, Taylor said. Within its data centers, it uses flash for caching, as a replacement for hard disks, and as an alternative to RAM.
In answer to another question, Taylor defended Facebook’s practices on deletion of customer data. When users delete their own data, it goes away everywhere on the company’s servers, he said. “We are absolutely committed to deleting data when we say we’re going to delete data,” Taylor said.