Apple’s Fusion Drive – What is It?

Lee Hutchinson, writing for Ars Technica:

“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.”

Translation: Fusion Drive storage will be faster than Seagate’s hybrid SSD/HDD drives, because OS X’s Core Storage actively manages the arrangement of files between the SSD component and the hard drive platters. Seagate’s hybrid technology simply uses flash memory as a cache for frequently accessed files. The files never fully “live” on the SSD component, frequently falling out of cache.

Apple has slowly rolled out new features based upon Core Storage, their storage management software delivered in OS X Lion. Their revamped File Vault full disk encryption is an example. The Fusion Drive, a hardware technology, relies upon Core Storage capabilities as well. All of this is invisible to users.

Early indications are that the hardware packaging is two separate drives: an SSD chip array and a familiar, 2.5-inch hard drive. If that’s the case, customers who purchased last year’s iMac with both SSD and HDD storage should be able to marry them into a Fusion Drive with OS X’s Disk Utility. There’s no obvious menu item for that right now, but stay tuned.

Is this a transitional technology, or will solid state drives eventually fully replace spinning hard drives? The first Fusion Drive incorporates a 1TB or 3TB hard drive. We’ll be hard-pressed to see solid state storage of that size at reasonable prices any time soon.

Why reinvent the wheel, anyway? Fusion Drive technology plays to the strengths of both storage types. Perhaps the answer is SSD-only for mobile platforms, and Fusion Drives for iMacs, Mac minis and Mac Pros where users are more likely to need or desire much larger volumes, and physical space can accommodate larger drive packages.