Facebook is now experimenting with a storage prototype that uses racks of Blu-ray discs instead of hard drives. The discs are held in groups of 12 in locked cartridges and are extracted by a robotic arm whenever they’re needed.
One rack contains 10,000 discs, and is capable of storing a petabyte of data, or one million gigabytes.
Tape will never be the whole answer to storing data, according to Dr Eleftheriou. But it forms a crucial part of a “storage hierarchy”. At the top of this are so-called hot data, those that need to be available for immediate access. These are best held in flash memory. Lukewarm data—those that people need to access frequently, but not instantaneously—are best stored on disks. Cold data, the stuff in long-term storage, can be recorded on tape. This cold store is by far the biggest repository. A report published in 2008 by Andrew Leung of the University of California, Santa Cruz, found that in general, 90% of an organisation’s data becomes cold after a couple of months.
The study essentially proves that, at least in the workplace, any amount of NAND memory larger than 10GB would have a limited impact on performance. Of course, data-intensive tasks like analytics or video rendering, where fresh data is being accessed all the time, would benefit from larger amounts of faster memory, but an average user is unlikely to notice the difference between SSD and SSHD.
Bcache is a Linux kernel block layer cache. It allows one or more fast disk drives such as flash-based solid state drives (SSDs) to act as a cache for one or more slower hard disk drives.
Hard drives are cheap and big, SSDs are fast but small and expensive. Wouldn’t it be nice if you could transparently get the advantages of both? With Bcache, you can have your cake and eat it too.
You can’t measure the capacity of the Internet from the last mile connection. Just because you have that 100-megabit or even one-gigabit connection from your house to some local data center doesn’t mean you are even going to get a five-megabit stream if you are getting service from a data center halfway across the country.
The download feature, which lets Comcast adopt an iTunes-ish model without the incremental pay-per-view component (for now), is a nice add-on because it lets users watch shows and movies on planes and in other venues that usually don’t have a solid enough broadband connection for streaming.