If you thought Netflix and iTunes would make optical discs a thing of the past, think again. Facebook has built a storage system from 10,000 Blu-ray discs that holds a petabyte of data and is highly energy-efficient, the company said Tuesday. Facebook said last year that it was exploring Blu-ray for its data-center storage needs, and on Tuesday it showed a prototype system at the Open Compute Project summit meeting in San Jose, California. It designed the system to store data that hardly ever needs to be accessed, or for so-called 'cold storage.' That includes duplicates of its users' photos and videos that Facebook keeps for backup purposes, and which it essentially wants to file away and forget. 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, said Jay Parikh, Facebook's vice president of infrastructure engineering, in a talk at the Open Compute summit. The company expects to be able to increase the capacity of the system to five petabytes over time, he said. Blu-ray discs are a good option for cold storage because they cost less to buy than hard disks and there's a lot of room for manufacturers to increase the storage density of Blu-ray, said Jason Taylor, Facebook's director of infrastructure, in an interview.