Introducing Apple File System Notes

Question

Eric Tamura - Manager, Local File Systems

Dominic Giampaolo - Senior Software Engineer, Storage / File Systems

What is Apple File System (APFS)?

Introduction:

Next generation file system
Runs on all four platforms - watchOS, iOS, macOS, tvOS
Scales from Apple Watch to Mac Pro
Designed to take advantage of Flash/SSD
Engineered with encryption as a primary feature

Motivation:

HFS+:

Apple wants to phase out HFS+
Data structures in HFS+ are single-threaded
Data structures are rigid - adding new features means a lot of backwards-compatibility and forwards-compatibility issues

APFS:

Designed for Apple products and ecosystem

Scale footprint from Apple Watch to Mac Pro

Other considerations:

Enhance security capabilities

Add new features!

Current File System Storage SW - watch video for overview.

All technologies currently in use will be replaced by APFS

This includes Core Storage. CS is being replaced by APFS <- Important for FileVault 2 encryption and Fusion drives

New Features:

Improved file system fundamentals

Flash / SSD-optimized
Crash-protected
Modern 64-bit native fields for inodes and metadata
Extensible design for data structure growth - addresses HFS+ rigid data structure issue by making sure that new features can be added without harming backwards compatibility. New fields can also be added.
Optimized for Apple software ecosystem
Low latency design, designed for fast responsiveness
Native encryption support - First class objects inside the file system

HFS Compatibility:

Support and replace HFS+ functionality

Three things not supported:

Exchange data
Directory hard links for Time Machine
Missed third item (watch video)

Space-sharing:

Watch video for multiple HFS+ partition space issue explanation

APFS containers:

Free space will dynamically resize as needed.

You can add more drive volumes to a container, to add free space to the container.

Cloning files and directories:

Cloning copies references to the data, rather than making a separate copy of the data.

When changes are made to the original, the changes are written elsewhere. This leaves the cloned copy alone with its existing references intact.

File system snapshots:

Makes read-only copy of the filesystem which stores the state of the filesystem at the time when the snapshot was taken.

Snapshots will take up disk space, to store that filesystem state. Snapshot maintenance is recommended, else you'll eventually run out of disk space.

Revert to snapshot - Filesystem will "rewind" to the state it was in when the snapshot was taken. Snapshot continues to exist and you can revert back as often as desired.

Fast directory sizing

How much space does a directory and its take up in the filesystem?

Users would like to know quickly.

Safely updating parent directory and included contents:

APFS stores the size of the directory / directories elsewhere in the filesystem - rather than in the directory itself.

Atomic Safe-Save (rename)

renamex_np (np = Non-POSIX)

Atomic-level saves to files and directories, rather than writing to temp files

Encryption:

HFS+ relies on CoreStorage to provide Full Disk Encryption

iOS relies on an HFS+ variant for encryption

APFS supports multiple levels of encryption

No encryption - no data is encryted
One key per volume (metadata and data) - This is equivalent to CoreStorage encryption today
Multi-Key encryption
Metadata encryption
Per-File encryption
Per-Extant encryption

Watch the video once available for more details on the encryption.

Command line tool - snapshotutil (available in Sierra Public Beta, not yet in Developer Previews)
Command line tool - mount_apfs - mounts APFS volumes

New APIs:

Foundation / File Manager (Swift)

- Automatically adopts new cloning and snapshot behavior when dealing with APFS volumes

libcopyfile

CoreOS library for copying hierarchies - supports cloning

Slightly above the POSIX layer

Introducing Apple File System Notes

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