The APFS filesystem

APFS is a new filesystem for iOS, macOS, tvOS, and watchOS. It is a 64-bit filesystem and supports over 9 quintillion files on a single volume. The following is a list of its main features:

• Clones: These are instantaneous copies of files or directories. Modifications are written elsewhere and continue to share the unmodified blocks; the changes are saved as deltas of the cloned file.
• Snapshots: Point-in-Time (PIT) read-only instances of the filesystem.
• Space sharing: This allows multiple filesystems to share the same underlying free space on a physical volume.
• Encryption: There are three modes, as follows:
  • No encryption
  • Single-key encryption
  • Multi-key encryption with per-file keys for file data and a separate key for sensitive metadata

Depending on the hardware, the Advanced Encryption Standard-XEX-based tweaked codebook mode with ciphertext stealing (AES-XTS) or the Advanced Encryption Standard-Cipher Blocker Chaining (AES-CBC) encryption mode is used.

• Crash protection: This is a novel copy-on-write metadata scheme; it's used to ensure that filesystem updates are crash-protected.
• Sparse files: These allow the logical size of files to be greater than the physical space they occupy on the disk.
• Fast directory sizing: This quickly computes the total space used by a directory hierarchy, allowing it to be updated as the hierarchy evolves.