What MacOS Sierra's New APFS File System Means to You

Sometime next year, Apple will start using a new file system on all its hardware. The new Apple File System (APFS) will replace Apple's old HFS+ file system, used on all Macs since 1998 which in turn was based on the archaic HFS, introduced in 1985.

APFS is an entirely new system designed for modern hardware and the cloud, and adds encryption, security, and reliability features that don't exist in Apple's older systems. Inevitably, like every other new file system, APFS will lead to compatibility issues, but Apple is giving itself plenty of time to smooth out the tangles before APFS is released to the public.

Your First Glimpse of APFS
For now, APFS is available in the developer beta of Apple's next-generation OS, macOS Sierra (the name OS X has been retired, but it's still OS X at heart). In the developer beta, you can create an APFS disk image, but you can't do much with it except copy files in and out, and you can't use an APFS disk as a startup disk. All that, presumably, will change when new Macs, iPhones, and iPads ship in 2017.

Better Security, Instant Cloning
Most users won't notice anything radically different about hardware with APFS on the hard disk, but a lot of subtle differences are hidden below the surface. Most notably, APFS uses integrated encryption instead of the essentially tacked-on encryption technique used by the existing OS X FileVault feature that slowly encrypts or decrypts an entire drive. APFS can encrypt whole disks and individual files with separate keys for the file and its metadata, giving granular control that could, for example, let individual users modify the data in a file without access to a separately encrypted audit trail of the changes.

APFS also makes possible instant cloning of folders and drives, and this technology is clearly going to add speed to Sierra's built-in feature that automatically backs up to iCloud any files on your Desktop and in your Documents folder. (Don't worry: you can disable this feature if you want to.) This feature already works with current hardware, but should be faster with APFS disks.

Nanosecond Precision, Better Backups
Apple's current file system time-stamps files with one-second precision, not enough to keep track of file changes with today's hardware. APFS time-stamps files with one-nanosecond precision, and this feature, combined with the technology used in the new cloning feature makes it easier to store multiple versions of a file in a minimum of space.

You can expect Sierra's version of Apple's Time Machine feature to take advantage of the new system for faster performance and more fine-grained backups. Incidentally, Microsoft built similar features into its NTFS technology years ago, and Mac users will now be able to benefit from the same kind of fast "shadow copy" technology used by Windows backup software.

Better Space Allocation
Other advantages of APFS disks include flexible space allocation, so that two APFS "disks" can borrow disk space from each other when they need it, and not be limited by the space allocated to them when they were created. APFS also builds in support for "sparse files"—files that don't fill all the allocated space on disk. (Older OS X versions already support sparse files, but in a clunky, developer-only way.) Also, thanks to its fast, built-in file handling, APFS promises sturdier safeguards against losing data in system crashes.

Optimized for Flash
Other under-the-hood features include optimization for flash storage, in contrast with the technologies in HFS+ that were designed for spinning-platter disks. Also, anyone who's ever waited impatiently for OS X to tell you how many megabytes are used by a folder will be glad to have APFS's "fast directory sizing" feature that keeps track of directory sizes on the fly. And if for some reason you intend to keep using your present Mac for the next 25 years, you'd better upgrade it to APFS before February 6, 2040, because the HFS+ file system won't be able to timestamp files after that date.

Recommended by Our Editors

10 Things You Need to Know About macOS Sierra

What About Drawbacks?
With all these advantages, what are the gotchas to watch out for? The biggest one is compatibility. If your Mac includes a Windows partition created by Apple's Boot Camp, you'll need a Windows driver that can read an APFS disk in the way that Apple provides a Windows driver that reads HFS+ disks. Presumably Apple will provide that driver before APFS goes public.

In the same way, developers and others who dual-boot their Macs between Sierra and older versions of OS X won't be able to access an APFS partition from a partition running the current El Capitan or earlier versions. But ordinary network access to and from an APFS drive won't be a problem because APFS supports the standard SMB network protocol used by Windows and everything else.

Don't Panic
Only developers need to worry about learning anything about APFS. For everyone else, the new file system promises better speed, enhanced security, and increased reliability. We'll keep reporting on APFS as the macOS betas include more and more of its features, but everything we've read about it makes us want it on our phones and computers as soon as possible.

You can get your hands on APFS this July when the public beta for macOS Sierra is released. In the meanwhile, you can read more about Apple's next operating system in 10 Things You Need to Know about macOS Sierra.