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How APFS in Mojave Affects Digital Storage Choices

Just as the file system under macOS works quietly, without fanfare, so do the preparations for the next update to Take Control of Your Digital Storage. We’re working on fleshing out the book for an update later this year, but in the meantime, I want to note a few areas where the march of technology has surpassed what’s in the current edition.

AFPS Everywhere

With the release of macOS Mojave in late 2018, APFS (Apple File System) is now the default file system for all Macs running the latest system, regardless of what type of storage the computer runs. Previously, APFS kicked in only for Macs running solid-state memory, like current laptop models. The exception was Fusion drives, which combine a traditional mechanical (spinning magnetic platters) drive for mass storage and SSD memory for caching frequently used files and the system itself to improve performance. (See the sidebar on page 57, “Which Filesystem for Which Drive?”)

This change has resulted in mixed performance—many people with iMacs and other computers with mechanical drives are seeing worse performance following the update. I’m hoping Apple is working through these issues, and we’ll see performance parity with whichever macOS update is announced at WWDC in June.

I still recommend formatting external mechanical drives as Mac OS Extended instead of APFS. Time Machine drives must still be Mac OS Extended, too.

APFS is a fascinating, deep change to macOS that should be invisible for most people, and I think it mostly succeeds at that. But when things go sideways, that can do so in weird ways. For example, the way it treats free space differently than before, leading to situations where your Mac reports a lot of available storage but an application sees far less. I wrote about this in a recent Seattle Times column, where the culprit was several invisible snapshots: Try these strategies to free storage on your Mac.

If you don’t yet own the book and are curious about just what I’m talking about, I recommend (a) buying the book!, or (b) read this TidBITS article: What APFS Does for You, and What You Can Do with APFS (and then buy the book!).

As I get further along with the book update, we’ll post more information here.

Posted by Jeff Carlson (Permalink)