Update: MacObserver has a nice simple explanation of how Fusion Drive works. All the magic is in OSX and Core Storage
Of all the things announced, the one I found the most interesting was the Fusion Drive.
On the hardware side, it’s a combination SSD and HD. That’s nothing really new, as hybrid SSD/HD’s have been around for a little while. Interestingly, most hybrid drives have a small SSD (~8GB) to use purely as a cache, Apple’s Fusion Drive apparently uses a 128GB SSD. ArsTechnica has a nice analysis, where they speculate that it’s an implementation of automatic tiering. When Phil Schiller first mentioned it in the presentation, I was thinking of Hierarchical Storage Management. Which I remember from my days of playing on Vaxen.
Clearly, there’s a software component to Fusion Drive that’s implemented in Mountain Lion, and ArsTechnica references something called “Core Storage”. The only other reference I could find to “Core Storage” was here and a one-liner in the OSX Lion release note under File Vault.
This seems like a fascinating solution, and I’m going to do more research to understand how it all works.