Apple File System
|Full name||Apple File System|
|Introduced||March 27, 2017 with iOS 10.3|
|Partition identifier||7C3457EF-0000-11AA-AA11-00306543ECAC (GPT)|
|Max. file size||8 EiB (263 bytes)|
|Max. number of files||263|
|Allowed characters in filenames||Unicode|
|Dates recorded||access, attributes modified, contents modified, created|
|Date resolution||1 ns|
|File system permissions||Unix permissions, NFSv4 ACLs|
|Supported operating systems||macOS, iOS, tvOS, and watchOS|
Apple File System (APFS) is a proprietary file system for macOS High Sierra and later, iOS 10.3 and later, tvOS 10.2 and later, and watchOS 3.2 and later, developed and deployed by Apple Inc. It aims to fix core problems of HFS+ (also called Mac OS Extended), APFS's predecessor on these operating systems. Apple File System is optimized for flash and solid-state drive storage, with a primary focus on encryption.
Apple File System was announced at Apple's developers conference (WWDC) in June 2016 as a replacement for HFS+, which had been in use since 1998. It was released for iOS devices on March 27, 2017, with the release of iOS 10.3, and for macOS devices on September 25, 2017, with the release of macOS 10.13.
The file system can be used on devices with relatively small or large amounts of storage. It uses 64-bit inode numbers, and allows for more secure storage. The APFS code, like the HFS+ code, uses the TRIM command, for better space management and performance. It may increase read-write speeds on iOS and macOS, as well as space on iOS devices, due to the way APFS calculates available data.
Clones allow the operating system to make efficient file copies on the same volume without occupying additional storage space. Changes to a cloned file are saved as deltas, reducing storage space required for document revisions and copies.
Apple File System natively supports full disk encryption, and file encryption with the following options:
- no encryption
- single-key encryption
- multi-key encryption, where each file is encrypted with a separate key, and metadata is encrypted with a different key.
Increased maximum number of files
Apple File System is designed to avoid metadata corruption caused by system crashes. Instead of overwriting existing metadata records in place, it writes entirely new records, points to the new ones and then releases the old ones. This avoids corrupted records containing partial old and partial new data caused by a crash that occurs during an update. It also avoids having to write the change twice, as happens with an HFS+ journaled file system, where changes are written first to the journal and then to the catalog file.
In its first generation, Apple File System does not provide checksums for user data, but does for metadata integrity. It also does not take advantage of byte-addressable non-volatile random-access memory, and does not support compression yet.
Unlike versions of HFS+ since Leopard, APFS has no support for hard links to directories. This is in line with many other modern file systems, but Time Machine still relies on them, so APFS is not yet an option for its backup volumes (as of macOS 10.13 High Sierra).
macOS High Sierra automatically converts the file system on devices with all flash storage to APFS. FileVault volumes are also converted, but Fusion Drives and hard disk drives are not. The primary user interface to upgrade does not present an option to opt out of this conversion, and devices formatted with the High Sierra version of APFS will not be readable in previous versions of macOS. Users can disable APFS conversion by using the installer's
startosinstall utility on the command line and passing
An experimental version of APFS, with some limitations, is available in the previous version of macOS (Sierra) through the command line
diskutil utility. Among these limitations, it does not perform Unicode normalization while HFS+ does, leading to problems with languages other than English. Drives formatted with Sierra’s version of APFS may also not be compatible with future versions of macOS or the final version of APFS, and the Sierra version of APFS cannot be used with Time Machine, FileVault volumes, or Fusion Drives.
APFS Retrofit Kit for macOS is a free system driver by Paragon Software which enables read-only access to APFS volumes under macOS 10.12 or earlier versions. For Mac users working on legacy versions of Mac OS X and macOS where APFS is natively not supported, the driver allows instant, read-only access to APFS-formatted data stored on hard disk drives, solid-state storage, or flash thumb drives.
iOS, tvOS, and watchOS
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- APFS’s “Bag of Bytes” Filenames
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