What is APFS?
Apple File System (APFS) is the file system Apple uses across macOS, iOS, iPadOS, watchOS and tvOS. It replaced HFS+ (Mac OS Extended), which dated from the 1990s. Apple announced APFS in 2016, and macOS Sierra included only a developer preview. It first shipped as the default in 2017: iOS 10.3 converted iPhones and iPads, and macOS High Sierra (10.13) converted Mac startup disks on SSDs. macOS Mojave (10.14) extended the conversion to Fusion Drives and hard drives.
Key features
- Containers and volumes: an APFS container can hold several volumes that share its free space, so you don't have to size each volume in advance.
- Snapshots: read-only, point-in-time copies of a volume. macOS uses them for system updates and Time Machine.
- Clones: copying a file on the same volume creates a clone almost instantly, and it takes no extra space until one copy changes.
- Copy-on-write metadata: changes go to new blocks instead of overwriting old ones, which protects the file system if the Mac crashes or loses power mid-write.
- Native encryption: built-in single-key or multi-key encryption, which FileVault uses on APFS Macs.
- Designed for flash storage, including TRIM support on SSDs.
Disk Utility offers APFS in plain, encrypted, case-sensitive, and case-sensitive encrypted variants. Since macOS Catalina (10.15), the startup disk is split into a read-only System volume and a separate Data volume for user files, both in one container.
Disk Utility and First Aid
Disk Utility shows the storage hierarchy: a physical disk contains an APFS container, and the container holds one or more volumes. Choose View, then Show All Devices to see every layer. When repairing with First Aid, go in this order, because each layer depends on the one below it:
- Run First Aid on each volume.
- Then run it on the container.
- If problems remain, run it on the physical disk.
To repair the startup disk, run Disk Utility from macOS Recovery.
APFS and other platforms
| File system | Native support | Notes |
|---|---|---|
| APFS | macOS High Sierra and later, iOS and iPadOS | Windows can't read it without third-party software |
| exFAT | macOS, Windows and most Linux systems | The usual choice for a cross-platform external drive |
| FAT32 | Almost every OS and device | 4 GB maximum file size |
| NTFS | Windows | macOS can read it but can't write to it without extra software |
For the CompTIA A+ exams
APFS is on the Core 1 (220-1201) acronym list, and this course covers Disk Utility with the macOS utilities for Core 2 (220-1202) objective 1.8. Know that APFS is the macOS file system, that an APFS drive won't work on a Windows PC without extra software, and that exFAT is the pick for sharing a drive between macOS and Windows. For First Aid, remember the order: volumes, then the container, then the disk.