Fusion Drive

Fusion Drive is Apple Inc.'s name for its implementation of a hybrid drive. Apple's implementation combines a hard disk drive with a NAND flash storage (solid-state drive of 24 GB or more) and presents it as a single Core Storage managed logical volume with the space of both drives combined.

The operating system automatically manages the contents of the drive so the most frequently accessed files are stored on the faster flash storage, while infrequently used items move to or stay on the hard drive. For example, if spreadsheet software is used often, the software will be moved to the flash storage for faster user access. In software, this logical volume speeds up performance of the computer by performing both caching for faster writes and auto tiering for faster reads.

The Fusion Drive was announced as part of an Apple event held on October 23, 2012 with the first supporting products being two desktops: the iMac and Mac Mini with OS X Mountain Lion released in late 2012. Fusion Drive remains available in subsequent models of these computers, but was not expanded to other Apple devices: the latest MacBook and Mac Pro models use exclusively flash storage, and while this is an optional upgrade for the mid-2012 non-Retina MacBook Pro still sold by Apple, it will replace the standard hard disk drive instead of complementing it in the fashion of Fusion Drive. Supported products have the following configurations:

Apple's Fusion Drive design incorporates proprietary features with limited documentation. It has been reported that the design of Fusion Drive has been influenced by a research project called Hystor. According to the paper, this hybrid storage system unifies a high-speed SSD and a large-capacity hard drive with several design considerations of which one has been used in The Fusion Drive.

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