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Is a Fusion Drive worth it?
QI intend to replace my iMac, and am considering a Fusion Drive rather than a hard disk?
AFusion Drives are an Apple-specific combination of a smaller SSD with a larger conventional hard disk. They attempt to deliver the speed of an SSD most of the time, at a cost which is little more than a hard disk.
To do that, macOS locks the two drives together using its Core Storage technology. This aims to keep your most active data – down to the block level, not necessarily whole files – on the SSD where they can be accessed most quickly, and less active ones on the hard disk with its far greater capacity. Fusion Drives used 128GB SSDs back in 2012, but now come in 24GB and 32GB versions.
Being two components, Fusion Drives will lose your data if just one part fails – much like a striped RAID array of two disks. As they’re peculiar to Apple, repairs and replacements normally have to be done by an Apple service provider, and may be more costly. That said, many Mac users have been enjoying the benefits of Fusion Drives for five years now, and most seem very reliable and effective.
Currently their biggest limitation is that High Sierra’s new file system, APFS, can’t beused on them, and they have to be kept in the older Mac OS Extended format. Apple is expected to deliver an update to High Sierra which will enable APFS’s use on Fusion Drives, although we don’t know when.
If you can afford a large SSD, that’s the best choice. But a Fusion Drive does deliver much better performance than a traditional hard disk, and is worth the extra cost.