What you need to know about APFS and macOS High Sierra compatibility

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On September 5, 2017, Apple published a technical note titled Prepare for APFS in macOS High Sierra. High Sierra will be available on September 25, and most of the questions we're getting about the new operating system revolve around the new Apple File System (APFS). Probably the most important information in the article from Apple is this quote:

Apple File System (APFS) is the default file system in macOS High Sierra for Mac computers with all-flash storage. APFS features strong encryption, space sharing, snapshots, fast directory sizing, and improved file system fundamentals.

When you install macOS High Sierra on the built-in solid-state drive (SSD) of a Mac, that drive is automatically converted to APFS. Fusion Drives and hard disk drives (HDDs) aren't converted. You can't opt out of the transition to APFS (our emphasis).

If you install APFS on any Mac that uses a solid-state drive (SSD) as a built-in boot drive, it will automatically convert to APFS and you will not have a choice. Those Macs that use Fusion Drives (like the iMac, for example) or regular hard disk drives (HHDs) will not be converted, period.

Here is the rest of the technical note verbatim:

APFS compatibility

Devices formatted as Mac OS Extended (HFS+) can be read from and written to by devices formatted as APFS.

Devices formatted as APFS can be read from and written to by:

  • Other devices formatted as APFS
  • Devices formatted as Mac OS Extended, if using macOS High Sierra

For example, a USB storage device formatted as APFS can be read by a Mac using High Sierra, but not by a Mac using Sierra or earlier.

APFS and FileVault

FileVault volumes are converted from Mac OS Extended to APFS, just like unencrypted volumes.

APFS and Boot Camp

Boot Camp doesn't read from or write to APFS-formatted volumes, but is compatible with High Sierra.

APFS and file sharing

  • Volumes formatted as APFS can't offer share points over the network using AFP.
  • APFS supports SMB and NFS, with the option to enforce only SMB-encrypted share points.

APFS and Time Machine

  • You don't need to change any Time Machine settings to back up APFS-formatted disks.
  • Any Time Machine share points must be shared over SMB instead of AFP.

So, one more time with feeling:

  1. SSDs will be converted to APFS whether you like it or not
  2. HDDs and Fusion Drives will NOT be converted to APFS
  3. APFS volumes can be read from and written to by other APFS devices and devices that are formatted as HFS+ and running High Sierra
  4. You can't run Boot Camp on an APFS-formatted volume
  5. For most people, Time Machine will work as usual with no changes

Have any questions? Leave 'em in the comments and we'll try to answer to the best of our knowledge at this time.