Is a Fusion Drive worth it?
I plan to replace my iMac. Should I consider a Fusion Drive instead of a hard disk?
Fusion Drives are an Applespecific 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 little more than that of 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.
With two components locked together in this way, Fusion Drives will lose your data if just one part fails — much like a striped RAID array of two disks. Since they’re peculiar to Apple, repairs and replacements normally have to be done by an Apple service provider, and might be more costly. That said, many Mac users have been enjoying the benefits of Fusion Drives for years now, and most seem very reliable and effective.
Currently their biggest limitation is that High Sierra’s new file system, APFS, can’t be used 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 that will enable the use of APFS 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 delivers much better performance than a traditional hard disk, and is worth the extra cost.