[mrpippy]

The 'Fusion' section at the end is interesting. macOS 10.13 didn't convert Fusion drives to APFS, but 10.14 will. Presumably this specific support for Fusion drives is new in 10.14.

HFS+ had no knowledge about Fusion drives, the caching was handled entirely at block-level by the lower CoreStorage layer (although later versions did add some flags so CoreStorage could pin metadata/swap blocks to the SSD).

Now what I'm really interested to see is if they open-source the filesystem driver along with the macOS 10.14 code drop. HFS+ (and its utilities) has always been open-source, last year APFS was not.

[arthurfm]

The only bad thing about Apple supporting APFS on Fusion Drives is that it gives them an incentive to continue selling future iMacs and Mac minis with Fusion Drives.

Having had to replace failed HDDs in Fusion Drive iMacs at work, it's certainly no fun. For all new Mac purchases I ensure they are SSD only now.

[mrpippy]

On that note, I am surprised that they added Fusion-awareness to APFS, rather than just putting APFS on top of CoreStorage.

It certainly is better to have the filesystem aware of the Fusion situation, but...measurably, significantly better? Would the experience have been significantly worse without it? 10.13 betas allowed APFS use on Fusion drives, presumably without any Fusion-awareness in the FS.

I'm surprised, but happy to see they did it.