Apple Fusion Drive - wait, what? How does this work?
Apple's new iMac announcement today included an interesting bit of information on an upcoming technology Apple calls "Fusion Drive." According to Phil Schiller this morning, the technology takes a relatively small solid state disk and a relatively large spinning hard disk drive, then "fuses" them together into a single drive.
Speculation in the Ars forums started immediately, with most wondering if "Fusion Drive" works the same as current hybrid disk drives. Those incorporate some amount of NAND flash inside a traditional hard disk drive as an extended cache. Others speculated the Apple technology resembles something like Intel's Smart Response Technology, which uses a dedicated SSD (of up to 64GB in size) as a transparent cache for a larger hard disk drive.
Technical details are scarce, but based on Schiller's descriptions, the answer to both of those questions appears to be "no." Apple's Fusion Drive does not appear to function like an SSD-backed disk cache, but rather seems more like a file-level implementation of a feature that has existed for some time in big enterprise disk arrays: automatic tiering.
