Apple File System is a new, modern file system for iOS, OS X, tvOS and watchOS. It is optimized for Flash/SSD storage and features strong encryption, copy-on-write metadata, space sharing, cloning for files and directories, snapshots, fast directory sizing, atomic safe-save primitives, and improved file system fundamentals.
The company notes that HFS+ and its predecessor HFS are more than 30 years old. These file systems were developed in an era of floppy disks and spinning hard drives, where file sizes were calculated in kilobytes or megabytes. Today, solid-state drives store millions of files, accounting for gigabytes or terabytes of data. There is now also a greater importance placed on keeping sensitive information secure and safe from prying eyes.
Apple feels that a new file system is needed to meet the current needs of Apple products, and support new technologies for decades to come.
Notably, APFS supports encryption natively. You can choose one of the following encryption models for each volume in a container: no encryption, single-key encryption, or multi-key encryption with per-file keys for file data and a separate key for sensitive metadata. APFS encryption uses AES-XTS or AES-CBC, depending on hardware. Multi-key encryption ensures the integrity of user data even when its physical security is compromised.
● Flash / SSD Optimization
APFS is optimized for Flash/SSD storage and can be used with traditional hard disk drives (HDD). A unique copy-on-write design uses I/O coalescing to maximize performance while ensuring data reliability.
● Space Sharing
Space Sharing allows multiple file systems to share the same underlying free space on a physical volume. Unlike rigid partitioning schemes, which pre-allocate a fixed amount of space for each file system, APFS volumes can grow and shrink without volume repartitioning.
Each volume in an APFS container reports the same available disk space, which is equal to the total available disk space of the container. For example, for an APFS container with a capacity of 100GB that contains volume A, which uses 10GB, and volume B, which uses 20GB, the free space reported for both volumes A and B is 70GB (100GB - 10GB - 20GB).
● Cloning of Files and Directories
A clone is a nearly instantaneous copy of a file or directory that occupies no additional space for file data. When a cloned file is modified, only the modified blocks are written to new locations on storage. In this way, the file system can store multiple revisions of the same document with less storage space.
A snapshot is a read-only instance of a file system on a volume. The operating system can use snapshots to make backups work more efficiently, and offer a way to revert changes to a given point in time.
● Fast Directory Sizing
Fast Directory Sizing allows APFS to quickly compute the total space used by a directory hierarchy, and update it as the hierarchy evolves.
● Atomic Safe-Save
Apple File System introduces a new Atomic Safe-Save primitive for bundles and directories. Atomic Safe-Save performs renames in a single transaction such that, from the user’s perspective, the operation either all happens or does not happen at all.
As a developer preview of this technology, there are currently several limitations:
● Startup Disk: APFS volumes cannot currently be used as a startup disk.
● Case Sensitivity: Filenames are currently case-sensitive only.
● Time Machine: Time Machine backups are not currently supported.
● FileVault: APFS volumes cannot currently be encrypted using FileVault.
● Fusion Drive: Fusion Drives cannot currently use APFS.
APFS is released as a Developer Preview in macOS 10.12, and is scheduled to ship in 2017.
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