Apple’s new so-called Fusion Drive technology is interesting. The cost of SSD drives is falling but not at a rate that consumers (or apparently Apple) would like. To that end, Apple engineers have come up with a novel solution that is proving to be a surprisingly effective middle-ground initiative. A Fusion Drive is comprised of two separate drive mechanisms. The first is an SSD drive 128GB or greater. The second drive is a conventional spinning hard drive, either 5400rpm or 7200rpm, now typically referred to as an HDD. The HDD can be pretty much any size, currently all the way up to 3TB.
What turns these two disparate drives into a Fusion Drive is the way they’re formatted. Apple’s Core Storage API includes the ability to effectively stripe the two drives into a single logical volume. Think of the single volume as a hybrid: the best parts of SSD (fast, fast, fast) with the best parts of the HDD (lots of cheap space). But what makes the Fusion Drive truly remarkable is what happens to the data on the drive automatically and invisibly once formatting is complete. Once the SSD and the HDD have been merged into a single Fusion Drive, the Mac OS becomes responsible for distributing the data across the two separate drive mechanisms. It does this allocation with intelligence. The most used data files, or files that benefit most from faster access times are stored on the SSD. Larger or lesser used files are stored on the HDD’s spinning platters. The idea being that the files on the SSD can be accessed more quickly, having vastly superior read and write times.