Community hub
0 subscribers7 pages, 0 posts
Recent from talks
All channels
Be the first to start a discussion here.
Be the first to start a discussion here.
Be the first to start a discussion here.
Be the first to start a discussion here.
Contribute something
Welcome to the community hub built to collect knowledge and have discussions related to Apple File System.
Nothing was collected or created yet.
Apple File System
View on Wikipediafrom Wikipedia
| Developer(s) | Apple Inc. |
|---|---|
| Full name | Apple File System |
| Introduced |
|
| Preceded by | HFS Plus |
| Partition IDs | 7C3457EF-0000-11AA-AA11-00306543ECAC (GPT) |
| Structures | |
| Directory contents | B-tree[1] |
| Limits | |
| Max file size | 8 Exabyte (9,223,372,036,854,775,808 bytes)[2] |
| Max no. of files | 9,223,372,036,854,775,808[2] |
| Allowed filename characters | Unicode 9.0 encoded in UTF-8[3][A] |
| Features | |
| Dates recorded | access, attributes modified, contents modified, created |
| Date range | January 1, 1970 – July 21, 2554[1] |
| Date resolution | 1 nanosecond[2] |
| File system permissions | Unix permissions, NFSv4 ACLs |
| Transparent compression | Partial (decmpfs)[4] |
| Transparent encryption | Yes[5] |
| Copy-on-write | Yes[3][5] |
| Other | |
| Supported operating systems | macOS, iPadOS, iOS, tvOS, watchOS, visionOS |
Apple File System (APFS) is a proprietary file system developed and deployed by Apple Inc. for macOS Sierra (10.12.4)[6] and later, iOS 10.3, tvOS 10.2,[7] watchOS 3.2,[8] and all versions of iPadOS.[9][10] It aims to fix core problems of HFS+ (also called Mac OS Extended), APFS's predecessor which had been in use since 1998. APFS is optimized for solid-state drive storage and supports encryption, snapshots, and improved handling of metadata integrity.[11][12]
History
[edit]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.[11][12] APFS was released for 64-bit 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.[13][8]
Apple released a partial specification for APFS in September 2018 which supported read-only access to Apple File Systems on unencrypted, non-Fusion storage devices. The specification for software encryption was documented later.[14]
Design
[edit]The file system can be used on devices with relatively small or large amounts of storage. It uses 64-bit inode numbers,[2] and allows for more secure storage by using a technology called Data Protection. 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,[8] as well as space on iOS devices, due to the way APFS calculates available data.[15]
Partition scheme
[edit]APFS uses the GPT partition scheme. Within the GPT scheme are one or more APFS containers (partition type GUID is 7C3457EF-0000-11AA-AA11-00306543ECAC). Within each container there are one or more APFS volumes, all of which share the allocated space of the container, and each volume may have APFS volume roles. macOS Catalina (macOS 10.15) introduced the APFS volume group, which are groups of volumes that Finder displays as one volume. APFS firmlinks lie between hard links and soft links and link between volumes.
In macOS Catalina the System volume role (usually named "Macintosh HD") became read-only, and in macOS Big Sur (macOS 11) it became a signed system volume (SSV) and only volume snapshots are mounted. The Data volume role (usually named "Macintosh HD - Data") is used as an overlay or shadow of the System volume, and both the System and Data volumes are part of the same volume group and shown as one in Finder.
Clones
[edit]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 delta extents, reducing storage space required for document revisions and copies.[10] There is, however, no interface to mark two copies of the same file as clones of the other, or for other types of data deduplication.
The feature is automatically available when a user copies any files using the Finder application, which is macOS's default file manager, but not when using the cp command.[16] To do that on the command-line, the cp utility on macOS has a -c parameter that allows it to use the clonefile system call.[17]
Snapshots
[edit]APFS volumes support snapshots for creating a point-in-time, read-only instance of the file system.[10]
Encryption
[edit]Apple File System natively supports full disk encryption,[2] 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.[10]
Increased maximum number of files
[edit]APFS supports 64-bit inode numbers, supporting over 9 quintillion files (263) on a single volume.[2][5]
Data integrity
[edit]Apple File System uses checksums to ensure data integrity for metadata but not for the actual user data, relying instead on error-correcting code (ECC) mechanisms in the storage hardware.[18]
Crash protection
[edit]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, an approach known as redirect-on-write. 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.[18]
Compression
[edit]APFS supports transparent compression on individual files using Deflate (Zlib), LZVN (libFastCompression), and LZFSE. All three are Lempel-Ziv-type algorithms. This feature is inherited from HFS+, and is implemented with the same AppleFSCompression / decmpfs system using resource forks or extended attributes. As with HFS+, the transparency is broken for tools that do not use decmpfs-wrapped routines.[19]
Space sharing
[edit]APFS adds the ability to have multiple logical drives (referred to as volumes) in the same container where free space is available to all volumes in that container (block device).[20]
Limitations
[edit]While APFS includes numerous improvements relative to its predecessor, HFS+, a number of limitations have been noted.
Limited integrity checks for user data
[edit]APFS does not provide checksums for user data.[21] It also does not take advantage of byte-addressable non-volatile random-access memory.[22][23]
Performance on hard disk drives
[edit]Enumerating files, and any inode metadata in general, is much slower on APFS when it is located on a hard disk drive (HDD). This is because instead of storing metadata at a fixed location like HFS+ does, APFS stores them alongside the actual file data. On SSDs, this fragmentation of metadata is inconsequential due to their lack of moving parts, but on HDDs, it leads to substantial performance degradation as the drive’s read/write heads must physically seek out scattered data fragments.[24]
Besides that, a key feature of APFS is "copy-on-write," which allows for rapid file duplication by creating references to the original data rather than copying it outright. This feature enables functionalities like snapshots and quick file copies. However, when files are modified after being copied, APFS creates new extents (data blocks) for the changes, leading to more fragmentation over time. This issue is exacerbated with applications like Time Machine, which creates multiple versions of files, further increasing fragmentation and slowing performance.[25] As a result, APFS is generally not recommended for use on HDDs, particularly for workloads involving frequent file modifications, copying, or snapshot usage.[26]
Compatibility with Time Machine prior to macOS 11
[edit]Unlike HFS+, APFS does not support hard links to directories.[3][27] Since the version of the Time Machine backup software included in Mac OS X 10.5 (Leopard) through macOS 10.15 (Catalina) relied on hard links to directories, APFS was initially not a supported option for its backup volumes.[28][27] This limitation was overcome starting in macOS 11 Big Sur, wherein APFS is now the default file system for new Time Machine backups (existing HFS+-formatted backup drives are also still supported).[29] macOS Big Sur's implementation of Time Machine in conjunction with APFS-formatted drives enables "faster, more compact, and more reliable backups" than were possible with HFS+-formatted backup drives.[30][31]
Security issues
[edit]- In March 2018, the APFS driver in High Sierra was found to have a bug that causes the disk encryption password to be logged in plaintext.[32]
- In January 2021, the APFS driver in iOS < 14.4, macOS < 11.2, watchOS < 7.3, and tvOS < 14.4 was found to have a bug that allowed a local user to read arbitrary files, regardless of their permissions.[33][34][35][36]
Support
[edit]macOS
[edit]An experimental version of APFS, with some limitations, is provided in macOS Sierra 10.12.4. It is available through the command line diskutil utility. Among these limitations, it does not perform Unicode normalization while HFS+ does,[37] leading to problems with languages other than English.[38] Drives formatted with Sierra’s version of APFS may also not be compatible with later versions of macOS or APFS, and the Sierra version of APFS cannot be used with Time Machine, FileVault volumes, or Fusion Drives.[39]
Since macOS 10.13 High Sierra, all devices with flash storage are automatically converted to APFS.[40] As of macOS 10.14 Mojave, Fusion Drives and hard disk drives are also upgraded on installation.[41] 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.[40] Users can disable APFS conversion by using the installer's startosinstall utility on the command line and passing --converttoapfs NO.[42]
FileVault volumes are not converted to APFS as of macOS Big Sur 11.2.1. Instead macOS formats external FileVault drives as CoreStorage Logical Volumes formatted with Mac OS Extended (Journaled). FileVault drives can be optionally encrypted.[citation needed]
iOS, tvOS, and watchOS
[edit]iOS 10.3, tvOS 10.2, and watchOS 3.2 convert the existing HFSX file system to APFS on compatible devices.[13][8][43]
Third-party utilities
[edit] | This section needs to be updated. The reason given is: Software companies have had a long time to update their software to support APFS. The article should reflect recent developments.. (August 2025) |
Despite the ubiquity of APFS volumes in today's Macs and the format's 2016 introduction, third-party repair utilities continue to have notable limitations in supporting APFS volumes, due to Apple's delayed release of complete documentation. According to Alsoft, the maker of DiskWarrior, Apple's 2018 release of partial APFS format documentation has delayed the creation of a version of DiskWarrior that can safely rebuild APFS disks.[44] Competing products, including MicroMat's TechTool and Prosoft's Drive Genius, are expected to increase APFS support as well.
| Name | Author | License | Mount | Read | Write | Repair | Format | Handle Encrypted | Notes |
|---|---|---|---|---|---|---|---|---|---|
| Paragon APFS SDK CE | Paragon Software Group | 4-Clause BSD License | No | Yes | No | No | No | No | Paragon has a write-capable commercial version of this SDK.[45] |
libfsapfs |
Joachim Metz | GNU LGPL v3 | FUSE | Yes | No | No | No | No | It has been packaged into Debian, Fedora Linux, Rocky Linux, Red Hat Enterprise Linux and Ubuntu software repositories.[46][47][48] |
apfs-fuse |
Simon Gander | GNU GPL v2 | FUSE | Yes | No | No | No | No | [49] |
linux-apfs-rw with apfsprogs |
Ernesto A. Fernández | GNU GPLv2 | Linux kernel module | Yes | experimental | Yes | experimental | No | [50] |
| Paragon's APFS for Windows | Paragon | Paid commercial | Windows driver | Yes | No | No | No | Not Apple T2 | [51] |
See also
[edit]Notes
[edit]References
[edit]- ^ a b Hansen, K.H.; Toolan, F. (September 21, 2017). "Decoding the APFS file system". Digital Investigation. 22: 107–132. doi:10.1016/j.diin.2017.07.003. ISSN 1742-2876.
- ^ a b c d e f "Volume Format Comparison". Apple Developer. Retrieved May 25, 2018.
- ^ a b c "Apple File System Guide / Frequently Asked Questions". Retrieved May 25, 2018.
- ^ Bertin, René. "Compression and APFS". Github. Retrieved February 2, 2019.
- ^ a b c Apple Inc. "Apple File System Guide (Features)". Retrieved December 16, 2023.
- ^ Vigo, Jesus (April 13, 2017). "How to set up and use Apple's APFS file system on macOS Sierra". TechRepublic.
- ^ "tvOS 10.2". What's New in tvOS. Apple Inc.
- ^ a b c d Warren, Tom (March 27, 2017). "Apple is upgrading millions of iOS devices to a new modern file system today". The Verge. Vox Media. Archived from the original on March 27, 2017. Retrieved March 27, 2017.
- ^ Roger Fingas (June 13, 2016). "'Apple File System' will scale from Apple Watch to Macs, replace HFS+". Apple Insider. Archived from the original on July 23, 2016.
- ^ a b c d Hutchinson, Lee (June 13, 2016). "Digging into the dev documentation for APFS, Apple's new file system". Ars Technica. Archived from the original on January 26, 2025. Retrieved February 25, 2025.
- ^ a b Weintraub, Seth (June 13, 2016). "Apple File System (APFS) announced for 2017, scales 'from Apple Watch to Mac Pro' and focuses on encryption". 9to5Mac. Archived from the original on March 28, 2017. Retrieved March 27, 2017.
- ^ a b Hutchinson, Lee (June 13, 2016). "New file system spotted in macOS Sierra [Updated]". Ars Technica. Condé Nast. Archived from the original on March 28, 2017. Retrieved March 27, 2017.
- ^ a b Clover, Juli (March 27, 2017). "Apple Releases iOS 10.3 With Find My AirPods, APFS, App Store Review Tweaks and More". MacRumors. Archived from the original on March 27, 2017. Retrieved March 27, 2017.
- ^ "Apple File System Reference" (PDF). Apple Developer.
- ^ Alan Loughnane (April 2017). "Updating your iPhone will give you one major benefit". joe.co.uk. Archived from the original on May 20, 2017.
- ^ "A ZFS developer's analysis of the good and bad in Apple's new APFS file system". Ars Technica. June 26, 2016. Retrieved February 17, 2025.
Side note: Finder copy creates space-efficient clones, but cp from the command line does not.
- ^ "[dedup] Use APFS clone (CoW) on macOS · Issue #219 · pkolaczk/fclones". GitHub. August 10, 2023. Retrieved February 17, 2025.
- ^ a b Adam Leventhal (June 19, 2016). "APFS in Detail: Data Integrity". Archived from the original on June 21, 2016.
- ^ Søgaard, Jens K. "How do I enable transparent compression on APFS?". Ask Different. Retrieved November 13, 2019.
- ^ Tamura, Eric; Giampaolo, Dominic (2016). "Introducing Apple File System" (PDF). Retrieved May 28, 2022.
- ^ "A ZFS developer's analysis of the good and bad in Apple's new APFS file system". Ars Technica. June 26, 2016.
- ^ Robin Harris (June 24, 2016). "Why Apple's APFS won't last 30 years". ZDNet.
- ^ Adam Leventhal (June 19, 2016). "APFS in Detail: Overview". Retrieved October 1, 2017.
- ^ "An analysis of APFS enumeration performance on rotational hard drives". Carbon Copy Cloner. Retrieved January 8, 2020.
- ^ "APFS Is Not Yet Ready for Traditional Hard Drives". Larry Jordan. December 3, 2017. Retrieved February 17, 2025.
- ^ Tim, OWC (November 29, 2017). "Using APFS On HDDs ... And Why You Might Not Want To". Rocket Yard. Retrieved February 17, 2025.
- ^ a b Leventhal, Adam H. (June 26, 2016). "A ZFS developer's analysis of the good and bad in Apple's new APFS file system". Ars Technica.
APFS right now is incompatible with Time Machine due to the lack of directory hard links, a fairly disgusting implementation that likely contributes to Time Machine's questionable reliability.
- ^ "Disks you can use with Time Machine". Retrieved December 17, 2019.
- ^ "APFS changes in Big Sur". June 29, 2020. Retrieved November 26, 2020.
- ^ "macOS Big Sur 11.0.1 Release Notes". Apple. Retrieved December 13, 2020.
- ^ Cunningham, Andrew (November 12, 2020). "macOS 11.0 Big Sur: The Ars Technica review". Ars Technica. Retrieved March 6, 2021.
- ^ "Uh Oh! Unified Logs in High Sierra (10.13) Show Plaintext Password for APFS Encrypted External Volumes via Disk Utility.app". mac4n6. March 21, 2018. Retrieved November 11, 2019.
- ^ "About the security content of iOS 14.4 and iPadOS 14.4 - Apple Support". Apple Support. Retrieved February 7, 2021.
- ^ "About the security content of macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave - Apple Support". Apple Support. Retrieved February 7, 2021.
- ^ "About the security content of watchOS 7.3 - Apple Support". Apple Support. Retrieved February 7, 2021.
- ^ "About the security content of tvOS 14.4 - Apple Support". Apple Support. Retrieved February 7, 2021.
- ^ Tsai, Michael J. "Michael Tsai - Blog - APFS's "Bag of Bytes" Filenames".
- ^ "APFS is currently unusable with most non-English languages". April 6, 2017. Archived from the original on June 8, 2017.
- ^ "How to Format a Drive With the APFS File System on macOS Sierra". Archived from the original on October 26, 2016. Retrieved October 26, 2016.
- ^ a b "Prepare for APFS in macOS High Sierra". Apple.com. September 7, 2017. Retrieved September 19, 2017.
- ^ "macOS 10.14 Mojave: The Ars Technica review". arstechnica.com. September 25, 2018. Retrieved December 20, 2018.
- ^ Trouton, Rich (September 26, 2017). "Using the macOS High Sierra OS installer's startosinstall tool to avoid APFS conversion". Der Flounder. Retrieved January 16, 2018.
- ^ "jakepetroules/Filesystem". GitHub. Retrieved March 29, 2017.
- ^ "DiskWarrior 5.2 & Apple File System (APFS)". Retrieved June 28, 2020.
- ^ "Paragon Software Group Releases Free Paragon APFS SDK Community Edition for Software Developers, OEMs, Forensic Experts". Paragon Software Group. GitHub
- ^ "libyal/libfsapfs". GitHub. November 7, 2019.
Library and tools to access the Apple File System (APFS)
- ^ "apfs-fuse - Fedora Packages". packages.fedoraproject.org. Retrieved October 20, 2022.
- ^ "apfs-fuse-20200928-1.el9.x86_64.rpm". rhel.pkgs.org.
{{cite web}}: CS1 maint: url-status (link) - ^ Ross, Alistair (February 23, 2019). "How to mount macOS APFS disk volumes in Linux". The Ultimate Linux Newbie Guide. (Github)
- ^ "linux-apfs/linux-apfs-rw: APFS module for linux, with experimental write support". GitHub. APFS for Linux. February 4, 2022.
- ^ "APFS for Windows | Paragon Software". Paragon Software Group. Retrieved January 29, 2024.
- ^ "libfsapfs/documentation/Apple File System (APFS).asciidoc at main · libyal/libfsapfs". GitHub. Retrieved May 30, 2025.
External links
[edit]- Apple Developer: Apple File System Guide
- Apple Developer: Apple File System Reference
- WWDC 2016: Introduction of APFS by Apple software engineers Dominic Giampaolo and Eric Tamura
- Detailed Overview of APFS by independent file system developer Adam Leventhal
iOS and iOS-based products | |||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Hardware |
| .svg){kind=small} | |||||||||||||||||||||||||
| Software |
| ||||||||||||||||||||||||||
| Services |
| ||||||||||||||||||||||||||
| Other | |||||||||||||||||||||||||||
Apple File System
View on Grokipediafrom Grokipedia
The Apple File System (APFS) is a proprietary file system developed by Apple Inc. for its operating systems, including macOS, iOS, iPadOS, tvOS, watchOS, and visionOS.[1] Introduced in 2017, APFS became the default file system replacing the Hierarchical File System Plus (HFS+), starting with macOS High Sierra (version 10.13) and iOS 10.3.[2] Optimized for flash and solid-state drive (SSD) storage, it emphasizes performance, security, and efficiency through features like strong cryptographic encryption, copy-on-write metadata, space sharing across volumes, file and directory cloning, and snapshots for point-in-time data preservation.[3][2]
APFS integrates encryption directly into its core design, enabling secure data protection across Apple's devices such as iPhone, iPad, Mac, Apple TV, Apple Watch, and Apple Vision Pro, without relying solely on separate tools like FileVault.[1] It uses a container-based structure where multiple volumes share disk space dynamically, allocating it on demand to optimize storage utilization on SSDs.[3] Compared to HFS+, APFS offers faster file operations, atomic safe-save mechanisms to prevent data corruption during writes, and improved resilience via snapshots that enable efficient backups and system recovery.[2] These capabilities make APFS particularly suited for modern Apple hardware, supporting both bootable and data volumes while maintaining compatibility with encrypted and non-encrypted configurations.[3]
History
Development and Introduction
The Apple File System (APFS) was developed as a successor to the Hierarchical File System Plus (HFS+), which had been in use since 1998 but exhibited significant limitations in the era of solid-state drives (SSDs) and modern storage demands. HFS+ was originally designed over 30 years ago for floppy disks and hard disk drives (HDDs), featuring single-threaded operations and rigid data structures that led to suboptimal performance on SSDs, including poor optimization for flash storage wear leveling and a lack of native support for features like snapshots.[4][5] These shortcomings, such as vulnerability to data corruption during interrupted writes and inefficiency with large-scale files in gigabytes, prompted Apple to initiate APFS development around 2014 to better support its ecosystem ranging from the Apple Watch to the Mac Pro.[6] The project was led by key engineers at Apple, including Dominic Giampaolo, a senior software engineer in storage and file systems who served as the lead architect, and Eric Tamura, manager of local file systems. Giampaolo, previously known for his work on the Be File System, brought expertise in modern file system design to the effort. APFS was publicly announced at Apple's Worldwide Developers Conference (WWDC) in June 2016, where it was presented as a from-scratch implementation optimized for SSDs and engineered with security in mind.[6][5] APFS was introduced as the default file system in macOS High Sierra (version 10.13), released on September 25, 2017, initially supporting SSD-based systems for both bootable and data volumes. At launch, Apple highlighted key initial features including strong encryption with multiple key options (per volume, per file, or per extent), native snapshots for point-in-time backups and system rollbacks, instant cloning of files and directories without full duplication, and space sharing to efficiently allocate storage across multiple volumes within a single container.[7][5] Support for HDDs and Fusion Drives was added in a subsequent update to macOS High Sierra (version 10.13.4) on March 29, 2018, extending APFS compatibility to traditional spinning drives. Adoption of APFS accelerated following its introduction, with the macOS High Sierra installer providing a nondestructive in-place conversion from HFS+ for existing SSD-based systems, making it opt-in for upgrades but mandatory for new installations on SSD boot volumes starting in 2017. For HDD-equipped Macs, users could opt in via manual formatting or later updates, while all new macOS installations post-High Sierra defaulted to APFS on compatible hardware to leverage its performance benefits. By macOS Mojave (10.14) in 2018 and subsequent releases, APFS became the required file system for booting on SSDs, solidifying its role across Apple's platforms.[4][7]Versions and Updates
The Apple File System (APFS) has evolved through successive macOS releases, with version numbers tied to the underlying build identifiers that reflect incremental improvements in functionality, performance, and security. APFS debuted in macOS High Sierra (10.13) in September 2017 with version 748.1.46, initially optimized for solid-state drives (SSDs) and converting compatible volumes automatically during installation. Subsequent updates within High Sierra refined this foundation, such as version 748.21.6 in 10.13.1, which addressed snapshot stability issues.[8] In macOS Mojave (10.14), released in September 2018, APFS advanced to version 945.200.129, introducing support for hard disk drives (HDDs) and restoring compatibility with Fusion Drives, which had been dropped in High Sierra. This update enabled broader hardware support while maintaining encryption and snapshot capabilities. By macOS Catalina (10.15) in 2019, version 1412.11.7 added System Volume Groups and firmlinks for separating system and data volumes, enhancing security isolation. macOS Big Sur (11) in 2020 brought version 1677.50.1, incorporating signed system volumes, native Time Machine backups to APFS-formatted drives, and optimizations for Apple Silicon. Monterey (12) used versions 1933.x.x and 1934.x.x, with minor refinements like trim-on-mount for better storage efficiency.[8][9] Later releases continued this progression: macOS Ventura (13) in 2022 adopted version 2142.x.x, improving compatibility for Time Machine backups with prior APFS volumes from Monterey and enabling trimming of unified disk read-write (UDRW) images as sparse files for more efficient external storage handling. macOS Sonoma (14) shifted to 2235.x.x (up to 14.3) and 2236.x.x (14.4 onward) in 2023–2024, with incremental performance tweaks; Sonoma 14.6 in July 2024 fixed an APFS privacy issue (CVE-2024-40783) by restricting data container access, preventing malicious apps from bypassing user privacy preferences. macOS Sequoia (15), starting with version 2311.x.x in 2024 and updated through 15.7 in 2025, included further security enhancements, such as improved state management in APFS to mitigate unauthorized access to sensitive user data (CVE-2024-54541). macOS Tahoe (16), released in September 2025, introduced version 24xx.x.x with additional refinements for storage efficiency and security, including better support for Apple Intelligence features and snapshot optimizations.[10][11][12] APFS maintains strong forward compatibility across macOS versions, allowing newer systems to read and write volumes created on older ones, though advanced features like system volume groups require macOS 10.15 or later. Conversely, macOS 10.12 Sierra and earlier can only read APFS volumes (via developer tools) but cannot write or boot from them, ensuring no downgrades without third-party conversion tools. Bootable APFS volumes demand macOS 10.13 or newer, while data volumes are supported starting from 10.13 for full read/write access.[3][9] On iOS, APFS launched in version 10.3 (2017) with basic snapshot support for efficient backups, evolving alongside macOS; iOS 17 (2023) enhanced snapshot handling for faster iCloud synchronization and device restores, leveraging APFS's copy-on-write mechanism to minimize data duplication during updates. iOS 18 (2024) and iOS 19 (2025) further optimized APFS for Apple Intelligence, improving backup efficiency and integration with on-device processing. These updates prioritize stability and security, with Apple recommending the latest tools for volume management to avoid compatibility pitfalls in multi-boot setups.[13][14]Architecture
Containers and Volumes
The Apple File System (APFS) employs containers and volumes as its core organizational structures to manage storage efficiently at the disk level. An APFS container represents a single logical entity that encompasses the entire physical disk or a designated partition, overseeing the allocation of blocks and metadata for all associated volumes. This design enables multiple volumes to coexist and dynamically share the available physical space, allowing each to expand or contract as needed without requiring fixed size allocations in advance.[2] Volumes function as logical partitions housed within an APFS container, where each operates as a distinct file system complete with its own independent namespace for organizing files and directories. Managed through the container's object map, volumes store their specific metadata, such as superblocks and file system trees, enabling isolated mounting and access. A container supports a maximum of 100 volumes, each assigned a unique virtual object identifier from the container's file system array.[15] In macOS, thediskutil list command distinguishes between internal physical disks, which represent the actual hardware storage devices (e.g., /dev/disk0), and synthesized disks, which are virtual entities created by APFS from one or more physical stores (e.g., /dev/disk1). The physical disk typically includes an APFS container partition (e.g., disk0s2, labeled as "Apple_APFS"), which APFS uses to synthesize the virtual disk that exports logical volumes such as Macintosh HD, Preboot, Recovery, and VM. This mechanism enables flexible volume management by abstracting the physical hardware into a dynamic, shared storage pool within the APFS container. "Internal" denotes built-in storage (as opposed to external), while "physical" versus "synthesized" reflects the hardware versus APFS-virtualized presentation.[16]
Starting with macOS 10.15 (Catalina), APFS introduces a specialized separation of the system volume and data volume to bolster system integrity and security. The system volume, designated with the role APFS_VOL_ROLE_SYSTEM, holds read-only operating system components and is sealed with cryptographic hashes to prevent tampering. In contrast, the data volume, marked as APFS_VOL_ROLE_DATA, accommodates mutable user files, applications, and other writable content. These volumes are logically combined into a volume group, appearing to users as a unified space while maintaining their distinct roles for protection.[17]
APFS containers support multi-boot configurations by accommodating multiple bootable system volumes within the same shared space, such as for stable and beta macOS installations, along with supporting volumes like preboot (APFS_VOL_ROLE_PREBOOT) and recovery (APFS_VOL_ROLE_RECOVERY). This setup allows efficient resource utilization across operating system instances without duplicating storage.[15]
Conversion from the legacy Hierarchical File System Plus (HFS+) to APFS entails creating a new APFS container on the target disk and migrating the existing HFS+ volumes into corresponding APFS volumes, ensuring no data loss through a structured process of metadata conversion, verification, and superblock updates. This non-destructive migration occurs automatically during upgrades to macOS High Sierra (10.13) or later, capitalizing on intentional architectural parallels between the two systems for seamless compatibility.[15]
Partition Scheme
The Apple File System (APFS) employs the GUID Partition Map (GPT) as its underlying partitioning scheme, which is the standard for modern macOS installations on Intel and Apple silicon-based Macs. This scheme divides the physical storage device into partitions, where APFS operates primarily within designated containers that function as logical partitions. GPT enables support for disks larger than 2 terabytes and provides robust identification through unique GUIDs, ensuring compatibility with the Extensible Firmware Interface (EFI) boot process.[18][15] APFS containers are identified by the partition type GUID7C3457EF-0000-11AA-AA11-00306543ECAC, labeled as "Apple_APFS" in tools like Disk Utility. Unlike traditional fixed-size partitions, APFS containers are resizable and allocate disk space dynamically on demand, allowing the container to grow or shrink without reformatting the underlying GPT structure. In macOS, this "Apple_APFS" partition serves as the physical store for the APFS container, which APFS synthesizes into a virtual disk presented in tools such as diskutil list as "synthesized" (e.g., /dev/disk1), distinct from the underlying "internal, physical" hardware disk (e.g., /dev/disk0). This UUID-based identification ensures uniqueness across devices and facilitates operations like cloning or migration, where the container's UUID remains consistent even as its physical boundaries adjust.[19]
Supporting partitions, such as the EFI system partition (GUID C12A7328-F81F-11D2-BA4B-00A0C93EC93B), coexist alongside the main APFS container to store bootloaders and firmware essentials.[15]
In the macOS boot process, the EFI system partition loads the initial bootloader, which then accesses the APFS container to mount the root volume and proceed with system initialization. Additional specialized APFS partitions, like the Preboot volume (GUID 69646961-6700-11AA-AA11-00306543ECAC) for storing kernel caches and the Recovery volume (GUID 52637672-7900-11AA-AA11-00306543ECAC) for diagnostic tools, integrate seamlessly within the GPT layout to support secure and efficient booting, particularly for encrypted volumes. This setup contrasts with the predecessor Hierarchical File System Plus (HFS+), which relied on the "Apple_HFS" partition type (GUID 48465300-0000-11AA-AA11-00306543ECAC) and required separate physical partitions for distinct volumes or functions, such as system and data areas. APFS streamlines this by consolidating multiple volumes into a single resizable container, eliminating the need for multiple dedicated partitions and enabling shared free space allocation for greater efficiency.[15]
Key Features
Cloning and Snapshots
APFS supports efficient cloning of files and directories through its copy-on-write (COW) mechanism, which enables instantaneous duplication without initially copying the underlying data blocks. When a file or directory is cloned, APFS creates a new inode referencing the same physical blocks as the original, marked by flags such asINODE_WAS_CLONED and INODE_WAS_EVER_CLONED in the inode structure.[15] This shared storage persists until modifications occur to either the clone or the original, at which point new blocks are allocated via COW to maintain data integrity.[15] Users can perform cloning at the command line using the cp -c option for files or cp -Rc for directories, ensuring space-efficient copies within the same volume.[20]
Snapshots in APFS provide read-only, point-in-time representations of an entire volume, capturing its state without duplicating data through the same COW architecture. These snapshots are created using the tmutil localsnapshot command or the fs_snapshot_create system call, allowing for quick generation typically in milliseconds regardless of volume size.[21] Once created, snapshots are stored as metadata records in the volume's B-tree structures, including details like creation time and extent references, and can be listed or deleted via Disk Utility or command-line tools like tmutil listlocalsnapshots.[22] They serve as the foundation for Time Machine local backups and enable rollbacks to previous states.[21]
At the core of both cloning and snapshots is APFS's block-based COW implementation, which organizes metadata and data extents in B-tree structures for efficient mapping and updates. The object map (omap) B-tree maps virtual object IDs to physical addresses, facilitating COW operations by redirecting writes to new locations while preserving historical references in snapshots.[15] Each volume supports a theoretical maximum of UINT32_MAX snapshots, though practical limits are imposed by available storage space and system resources.[15] Exemptions from COW, such as for certain system files, are tracked via extended attributes to ensure compatibility.[15]
A primary use case for APFS snapshots is during macOS system updates, where the installer automatically creates a snapshot before applying changes, allowing users to revert to the pre-update state if issues arise.[21] This feature enhances reliability for software installations and maintenance tasks, such as restoring from local snapshots in recovery mode.[22]
Encryption and Security
APFS provides native support for full-volume encryption, utilizing the AES-XTS algorithm with either 128-bit or 256-bit keys depending on the hardware.[23] This encryption is applied at the file system level, protecting both file data and metadata across volumes.[15] On devices with A14 through A18 or M1 through M4 processors, APFS employs AES-256 in XTS mode, where a 256-bit per-file key is subdivided for per-extent encryption to enhance granularity and performance.[23] Older hardware, such as A9 through A13 or S5 through S9, uses AES-128 in XTS mode with corresponding 128-bit tweaks and cipher keys.[23] This built-in capability integrates seamlessly with FileVault, Apple's full-disk encryption feature, which leverages APFS to secure all data at rest on the boot volume without requiring additional third-party tools. Key management in APFS relies on a hierarchical structure centered around volume encryption keys (VEKs) and key encryption keys (KEKs). Each APFS volume is created with a default VEK that encrypts its contents, including metadata, while per-file keys—derived and managed by the Secure Enclave—are used for individual file protection.[15] These keys are generated using a true random number generator within the Secure Enclave and can be derived from user credentials, such as passwords or passcodes, via PBKDF2 with high iteration counts (typically 100,000 or more, such as 100,000, 117,590, or 127,270 using PBKDF2-HMAC-SHA256), which makes each password check slow (0.5–2 seconds on modern Macs) to resist brute-force attacks despite allowing unlimited attempts without lockout or wipe; this mechanism applies to APFS-encrypted external drives created via macOS Disk Utility.[24][25][26] These keys can also be derived from hardware-bound unique identifiers (UIDs) tied to the device. Multi-key support is enabled through keybags, which store multiple wrapped keys (e.g., user, device, escrow, or iCloud recovery keys) associated with volume group UUIDs, allowing flexible access control and recovery options without exposing plaintext keys to the application processor.[15] On Macs with T2 chips or Apple Silicon, the Secure Enclave handles key derivation and storage, ensuring keys remain isolated and protected even if the main storage is removed.[23] APFS defines security levels through Data Protection classes, mapped to numeric identifiers: SL 1 (Class A, Complete Protection), SL 2 (Class B, Protected Unless Open), SL 3 (Class C, Protected Until First User Authentication), SL 4 (Class D, No Protection), and additional classes like SL 6 (Class F) or SL 14 (Class M) for specialized uses. These levels determine file accessibility based on device state—such as locked, after first unlock, or during specific operations—with keys unlocked progressively via user authentication.[23][27] SL 1 provides the highest protection, requiring authentication before access and becoming inaccessible shortly after the device locks, while SL 3 (the default for most user data on modern Apple Silicon devices) becomes accessible after the first user authentication following reboot and remains accessible until the next reboot. In modern macOS on Apple Silicon devices, the default is SL 3 (Class C), balancing accessibility and security for most user data after initial unlock.[23][27] To optimize performance, APFS leverages hardware acceleration via dedicated AES engines in Apple Silicon SoCs and T2 security chips, enabling inline encryption and decryption of NAND flash storage without software overhead.[23] This hardware integration ensures that cryptographic operations occur transparently during I/O, with keys never exposed outside the Secure Enclave, thereby maintaining high throughput even for encrypted volumes. For external or unsupported storage, APFS falls back to software-based encryption, but internal volumes on compatible hardware benefit from this acceleration for efficient full-volume protection.[15]Compression and Space Sharing
APFS supports transparent inline compression applied to individual files, which reduces overall storage space usage and minimizes write operations to extend the lifespan of SSDs. This compression is handled automatically by the file system without user intervention, allowing files to be stored in a compressed form on disk while appearing uncompressed to applications. The algorithms employed include LZVN for fast compression suitable for Apple platforms, LZFSE for efficient compression, and Zlib for balanced performance across systems.[28] A key aspect of APFS is space sharing, where multiple volumes within a single container dynamically share the available free space without fixed quotas or pre-allocated partitions. This allocation occurs automatically as needed, with the space manager allocating and freeing blocks across volumes to optimize storage efficiency. Unlike traditional partitioning schemes, this approach eliminates wasted space from underutilized volumes and simplifies management in multi-volume environments.[29][30] APFS imposes generous theoretical limits to support massive datasets, allowing up to 9 quintillion files per volume and a maximum volume size of 8 exabytes. These limits stem from the file system's 64-bit architecture, enabling scalability for large-scale storage needs on modern hardware.[31][29] In multi-volume setups, such as the separation of system and data volumes in macOS 10.15 and later, space sharing provides efficiency by allowing the read-only system volume and writable data volume to dynamically utilize the container's shared pool without rigid size constraints. This design enhances storage utilization while maintaining logical separation for security and maintenance purposes.[1][30]Data Protection
Integrity Mechanisms
APFS ensures the integrity of its metadata through the use of checksums embedded in every file system object. Each object includes a Fletcher-64 checksum, a non-cryptographic hash computed over the object's data excluding the checksum field itself, stored in theo_cksum field of the obj_phys_t structure. This 8-byte checksum is verified during read operations to detect any alterations or corruption in metadata blocks, such as those representing B-trees, inodes, and other structural elements. The Fletcher-64 algorithm, consisting of two 32-bit accumulators, provides efficient detection of errors with low computational overhead, suitable for frequent metadata access.[15]
In contrast to metadata, user data blocks in APFS do not receive file system-level checksumming, relying on the error-correcting code (ECC) capabilities of the underlying NAND flash hardware for bit error detection and correction. This design choice balances integrity assurance with the efficiency demands of modern SSDs, where metadata—being smaller in volume—is prioritized for checksum validation to safeguard overall file system consistency.[15][32]
Additionally, the Signed System Volume (SSV), introduced in macOS Big Sur, uses SHA-256 cryptographic hashes in a Merkle tree structure to verify the integrity of both system metadata and data, with a root seal checked at boot to prevent tampering.[33]
A core integrity mechanism in APFS is its copy-on-write (COW) approach to metadata modifications, which eliminates the risk of partial writes that could corrupt structures during power loss or crashes. When updating metadata, such as an inode or B-tree node, APFS allocates a new block, copies the unchanged portions, applies modifications, computes the checksum, and writes the new version to disk. Only after successful writing does the file system update the parent pointer to reference the new block, leaving the original intact until garbage collection. This atomic update process, combined with periodic checkpoints that snapshot the container's root state, ensures that the file system always mounts to a consistent, valid configuration without requiring fsck repairs in most failure scenarios.[15]
APFS eschews traditional journaling mechanisms found in predecessors like HFS+, opting instead for COW and checkpoints to achieve equivalent or superior consistency guarantees for metadata. HFS+ employed a dedicated journal to log and replay pending transactions, but this introduced overhead and vulnerability to journal corruption. In APFS, the absence of journaling reduces write amplification on flash media while leveraging COW to provide transactional semantics inherently, resulting in stronger metadata protection overall. However, this shift means user data lacks the proactive integrity logging of HFS+, placing greater emphasis on storage-level reliability for long-term data preservation.[15]
Crash Protection
The Apple File System (APFS) employs a copy-on-write (COW) metadata scheme to provide robust crash protection, ensuring that file system updates are atomic and consistent even in the event of power failures or system crashes. Unlike traditional journaling file systems, which incur a "write-twice" overhead by logging changes before committing them, APFS's COW approach modifies metadata by writing new versions to unused space rather than overwriting existing data. This mechanism guarantees that operations such as file creation, deletion, or directory renames either complete fully or roll back entirely, preventing partial updates that could lead to inconsistencies.[29][15] APFS further enhances recovery through snapshot-based mechanisms, where the file system maintains read-only snapshots of volumes at key points, such as during boot or major updates. In the case of a crash, the system can automatically revert to the most recent valid snapshot or checkpoint, restoring a consistent pre-crash state without data loss. These snapshots are integral to bootable volumes in macOS, allowing the recovery partition to mount and repair from a known-good state if the primary volume is compromised. This design leverages the container's space management to store ephemeral objects that protect against interruptions, ensuring quick and reliable recovery on SSD storage.[15][22] For post-crash repair, APFS includes thefsck_apfs utility, which scans and fixes inconsistencies by verifying redundant metadata structures like checkpoints, B-trees, and object maps. The tool uses transaction identifiers (xids) to validate the integrity of ongoing operations, repairing issues such as orphaned inodes or mismatched snapshots without requiring full volume scans in most cases. It operates in modes for checking, repairing, or dry-running, and is invoked automatically by Disk Utility's First Aid or manually in recovery environments.[34][15]
While APFS's COW and snapshot features offer efficient crash protection tailored to flash storage, they introduce some performance considerations during intensive write operations on SSDs. The need to allocate new blocks for each modification can increase CPU usage for metadata management, particularly under heavy workloads like large file copies or frequent updates, though this is mitigated by in-memory caching for ephemeral objects. Overall, this approach avoids the I/O penalties of journaling while maintaining strong consistency.[29][15]
Limitations
Performance Characteristics
APFS is optimized for solid-state drives (SSDs), leveraging features like TRIM support to maintain high performance by allowing the operating system to inform the SSD of unused blocks for efficient garbage collection. This integration helps sustain consistent read and write speeds, particularly as the drive fills. The file system's copy-on-write (COW) metadata scheme further aids SSD wear leveling by minimizing write amplification, distributing data blocks to avoid concentrated wear on specific cells. Apple's documentation highlights that these optimizations enable high-performance parallelized metadata operations.[2][35][36] On hard disk drives (HDDs), APFS faces notable limitations stemming from its COW-based random access patterns, which promote metadata and file fragmentation over time. This results in excessive seek operations by the mechanical read/write head, degrading performance for operations involving scattered data. Independent analysis shows file enumeration times on APFS-formatted HDDs ranging from 3 to 20 times slower than on HFS+-formatted equivalents, with initial listings taking about 80 seconds versus 20-27 seconds, worsening to 300-380 seconds after repeated cycles. Due to these issues, Apple has not recommended APFS for mechanical drives in versions prior to 2018 updates, as the system's design prioritizes flash storage characteristics.[37][38] APFS provides built-in defragmentation that can be enabled via command-line tools, such asdiskutil apfs defragment, along with opportunistic defragmentation for files exceeding 20 MB during access. However, these features do not significantly improve performance on HDDs. APFS lacks support for third-party defragmentation tools traditionally used with HFS+. As of macOS 26 (Tahoe) in 2025, performance issues on rotational media persist.[39][40][2][41][42]
For key metrics, file creation and deletion on SSDs benefit from near-instant COW clones, often completing in milliseconds, while on HDDs these operations can extend to seconds due to physical constraints.
Compatibility Issues
Prior to macOS Big Sur (version 11, released in 2020), Time Machine backups on APFS-formatted volumes were incompatible with native APFS snapshots, necessitating a workaround using a sparsebundle disk image to emulate an HFS+ file system within the APFS container.[43] This approach relied on hard links for efficient incremental backups but introduced overhead and limitations, such as the inability to leverage APFS's direct snapshot capabilities.[44] With the introduction of Big Sur, Time Machine gained native support for APFS volumes, enabling faster and more efficient backups without the sparsebundle intermediary.[45] APFS provides native read and write support exclusively on Apple platforms, including macOS, iOS, iPadOS, tvOS, and watchOS, due to its proprietary design optimized for these ecosystems.[1] On non-Apple operating systems like Windows or Linux, APFS volumes are not natively readable or writable, requiring third-party drivers—such as Paragon APFS for Windows—for access, where read support is generally available but write functionality remains limited and may not fully support advanced features like snapshots or encryption.[46] Downgrading an APFS volume to HFS+ (Mac OS Extended) is not possible through non-destructive conversion, as the file systems have fundamentally different structures; reverting requires erasing the volume entirely via Disk Utility, which deletes all data and necessitates a full backup and restore process beforehand.[47] This limitation stems from APFS's container-based architecture, which cannot be directly mapped back to HFS+ without reformatting the underlying physical disk or partition.[48] Some legacy applications encounter compatibility issues when running on APFS volumes, particularly in early implementations like macOS High Sierra, due to differences in how extended attributes and file metadata are handled compared to HFS+.[49] For instance, Adobe Illustrator CC 2017 exhibited launch failures and file access problems on APFS-formatted drives, as the software relied on HFS+-specific behaviors for extended attributes that were not yet fully compatible.[49] In APFS, extended attributes are stored separately from file inodes and data, which can disrupt older apps expecting integrated metadata storage, though subsequent macOS updates and app patches have mitigated many such issues.[50] As of 2024, APFS continues to have incompatibilities including the expansion of sparse files when moved or copied, the loss of clone file preservation during such operations, the inability to copy snapshots in backups, and lack of support for directory hard links.[51]Platform Support
macOS Integration
Apple File System (APFS) has been the default file system for all new installations of macOS High Sierra (version 10.13) and subsequent releases on Mac computers equipped with flash or solid-state storage. This shift prioritizes APFS's optimizations for SSDs, including features like snapshots and space sharing, while maintaining compatibility with external and mechanical drives formatted in other systems. For users upgrading from earlier macOS versions, the installer automatically converts compatible HFS+ volumes on solid-state drives to APFS non-destructively, preserving data and enabling seamless adoption without manual intervention.[3] macOS integrates APFS with platform-specific security enhancements, notably signed system volumes introduced in macOS Catalina (10.15). This mechanism splits the boot volume into a read-only system volume and a writable data volume within an APFS container, using cryptographic hashes and a Merkle tree structure to verify file integrity and prevent tampering. APFS snapshots underpin this by supporting atomic updates and rollback if installations fail, ensuring system stability. In macOS Big Sur (11.0) and later, the signed system volume incorporates sealed snapshots, which mount the OS read-only with a cryptographic seal verified at boot, further bolstering protection against malware and unauthorized changes.[52] APFS volume management in macOS is facilitated through built-in tools tailored for user accessibility and advanced control. Disk Utility offers a graphical interface for creating, resizing, erasing, and deleting APFS volumes within containers, with options to set quotas or reserves for space allocation and view snapshots directly. For command-line operations, thediskutil utility provides APFS-specific verbs, such as diskutil apfs addVolume to create new volumes, diskutil apfs cloneVolume for efficient cloning via copy-on-write, and diskutil apfs snapshot to generate point-in-time snapshots for backups or testing. These tools enable precise handling of APFS features like encryption and cloning without third-party software.[53][19]
As of macOS Sequoia 15.7.2 (November 2025), APFS receives full native support across all compatible hardware, serving as the exclusive file system for boot volumes on Apple Silicon Macs (M-series chips and later). APFS continues to serve as the foundational storage layer for macOS, with no alternatives available for internal system volumes on these devices.[54]