Things have suddenly become more complex when supporting Macs, thanks to High Sierra’s semi-adoption of the new Apple File System, otherwise known as APFS.

For over 30 years all Macs have used Apple’s HFS file system, which last underwent changes in 1998 when HFS+ was introduced (a.k.a. Mac OS Extended).  A file system is the behind-the-scenes mechanism controlling how a volume is formatted, and how the operating system stores or retrieves data.  HFS+ was also the base file system for iOS, tvOS, and watchOS.

APFS is Apple’s replacement for the aging HFS+ file system.  APFS offers many long-awaited improvements including: Support for snapshots, native full disk encryption, delta based file copy (copies of files don’t occupy additional storage space), advanced crash protection, and shared space across multiple volumes.

HFS+ volumes can be converted to APFS, but they can’t be converted back.  Any iPhone or iPad running iOS 10.3 or later has already had its storage converted to APFS.  The same is true with any recently updated Apple TV or Apple Watch.

I believe APFS will ultimately improve all things Apple, but mark my words… From a Mac troubleshooting and support perspective, APFS is the biggest change Apple has made since switching from PowerPC to Intel processors.  It adds a layer of complexity to supporting Macs unlike no other.

Mac savvy engineers should know the following about APFS:

  1. High Sierra only converts SSD boot volume to APFS, HDD and Fusion Drives are not converted… more
  2. Because High Sierra can run on either APFS or HFS+, determining the file system has become an important troubleshooting step… more
  3. APFS volumes cannot be used for Time Machine backups… more
  4. AFP file shares cannot be created on an APFS volume… more
  5. External drives formatted as APFS cannot be mounted on Macs running Mac OS 10.11 or older