Jens Lodholm

Disaster Averted with APFS

An announcement interrupts your TV show. “That was close,” the president declares.

What is he talking about? you wonder.

“Earlier today, an asteroid designated ‘1999 RQ36,’ was diverted from its collision course with earth. Using a classified unmanned payload referred to as the Asteroid Prevention Flight System, or ‘APFS’, SpaceX succeeded in its mission to prevent what would undoubtedly have been a catastrophic event. This was the third such attempt.

“Efforts to divert this object have been in progress for 14 months, but to avoid widespread panic, knowledge of the impending collision was kept secret until we could prevent its impact. The object’s new trajectory has been confirmed as safe, and it will clear the earth.”

You don’t know whether to be upset or glad. The earth will not be destroyed! But the government hid the truth from us. At least they were hard at work preventing disaster. What other disasters have they prevented?

While this fictional scenario overstates the case quite a bit, Apple has been quietly developing a system designated ‘APFS’—the Apple File System. It addresses problems most Mac users aren’t even aware of, but soon it will benefit us all.


Apple’s 1998 rollout of the current HFS+ disk file system radically improved storage efficiencies, but rendered previous disk utilities obsolete. Using such utilities could make disks unrecoverable, and Apple’s Disk First Aid was relatively ineffectual. The then-leader in Mac disk repair, Symantec, dawdled on a compatible version, stranding Mac professionals until new tools arrived.

The years since have seen groundbreaking technology changes: the advent of OS X with its UNIX undercarriage; migration of peripheral interfaces from SCSI/ADB to Thunderbolt/SATA/USB; the adoption of WiFi; increased disk sizes; the life-changing simplicity of Time Machine; increased awareness of security leading to disk encryption; the creation of iOS devices; and widespread inclusion of much faster flash/SSD storage.

These developments, coupled with users’ constant desire for speed, disk space, and reliability, highlight the need for a new foundation at the disk level. While you may not have noticed, Apple did. Its engineers have been busily preparing APFS against an impact we didn’t even give thought to.


Speed - When asked to copy an item, APFS’s new Clones feature instead refers to the original file and only records differences from it. Fast Directory Sizing yields folder size info much more quickly.

Disk Efficiency - By tracking changes, Clones also saves disk space. Snapshots improves Time Machine backups by saving a view of the file system at a specific point in time. Sparse Files use empty disk space more economically.

Reliability - Copy-on-Write protects against crashes and other disk interruptions without the journaling overhead of HFS+. Checksums provide quick indicators of file integrity.

Security - New customizable encryption methods provide easy-to-use protection.

Accuracy - Improved file operations now yield better time stamps and renaming operations.

Limitations (Current)

Because APFS is still officially in beta testing as of this writing, marked (*) features may yet be reversed by the final release.

  • Unavailable for Startup disks*
  • Incompatible with Older Mac OS versions
  • Incompatible with Boot Camp partitions*
  • Incompatible with current third-party disk utilities
  • Case-sensitive naming*
  • No Time Machine to APFS disks*
  • No FileVault on APFS disks* - Though it may not be called FileVault, encryption will be available.
  • Not available on Fusion drives*
  • Data deduplication not supported - The possibility of encryption prevents this, but  space-saving measures such as Clones render this unnecessary.

What to Expect

Apple has declared an official release for APFS of 2017. Most of its bugs should disappear by then, as well as some of its limitations. Expect Apple to release the appropriate software tools for the new format; startup disks should even allow migration in place.

If the rollout of APFS follows that of HFS+, plan to upgrade your favorite third-party disk utilities or adopt new ones. But since Apple’s modern Disk Utility is much better than Disk First Aid ever was, and drives now need less repair than before, we might all be surprised.

Undoubtedly APFS will have technical challenges. Your best tool is information. Stay up on industry trends by regularly checking Mac support resources and Mac news sites.

For more information on APFS, consult Apple’s official documentation: <>