After many years and at least one false start, Apple announced at WWDC last year that it would begin shipping a new, modern file system in 2017. Dubbed APFS (for Apple File System), it is designed to improve support for solid-state storage and encryption and to safeguard data integrity. When released, it will finally replace the nearly two-decade-old HFS+ filesystem that Apple has been tacking new features onto since 1998.
An early version of APFS was included in macOS Sierra as a beta for developers to experiment with, but it was intentionally limited in some important ways; it couldn’t be used as a boot drive, it didn’t support Fusion Drives, and you can’t back up APFS volumes with Time Machine. We weren’t expecting to hear more about a final APFS rollout until this year’s WWDC, but it looks like Apple is getting ready to start the party already: according to the beta release notes for iOS 10.3, devices that are upgraded will automatically have their HFS+ file systems converted to APFS. From the release notes:
When you update to iOS 10.3, your iOS device will update its file system to Apple File System (APFS). This conversion preserves existing data on your device. However, as with any software update, it is recommended that you create a backup of your device before updating.
Apple’s stated end goal is to perform an in-place file system conversion for all its currently supported devices, including all Macs, iPhones, iPads, iPods, Apple TVs, and Apple Watches. iOS 10.3 will provide some early information on how reliable that conversion will be.
It’s an approach that makes sense; there are way more iDevices than Macs out there, which would increase the number of affected users if anything goes wrong. But iOS doesn’t give users direct control of the file system or of their devices’ partition maps, so it’s a reasonably safe, controlled environment. Macs can have a wider variety of partition and file system setups, increasing the likelihood that some edge case will throw things off. There’s no suggestion in the macOS 10.12.4 release notes that any drives will be converted to APFS, and we may need to wait for the next major release of the operating system before that starts happening.