Apple have updated the online support documentation to give more details about the new file system (APFS) that is coming with the next generation of the operating system High Sierra. Apple File System (APFS), is the default file system in macOS High Sierra for Mac computers with all flash storage, it is designed to scale from an Apple watch to a Mac Pro.

Apple File System is a new, modern file system for iOS, macOS, 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. APFS replaces HFS+ as the default file system for iOS 10.3 and later, and macOS High Sierra and later.

A few things that might be important to note.

• When you upgrade to macOS High Sierra, systems with all flash storage configurations are converted automatically. Systems with hard disk drives (HDD) and Fusion drives won't be converted to APFS. You can't opt-out of the transition to APFS.
• FileVault volumes are converted from HFS+ to APFS, just like unencrypted volumes.
• Devices formatted as HFS+ can be read and written to by devices formatted as APFS.
• Devices formatted as APFS can be read and written to by any APFS-formatted devices but only by HFS+ formatted devices running macOS 10.12.6 or later.
• Volumes formatted with APFS can't offer share points over the network using AFP. SMB and NFS are supported when using APFS. The option to enforce only SMB-encrypted share points is also available.

What are the advantages?

• APFS supports 64-bit inode numbers, supporting over 9 quintillion files on a single volume
• APFS is optimized for SSD storage, it will work with traditional hard disk drives as well.
• No need to repartition, APFS allows Space Sharing, which lets multiple file systems share the same underlying free space on a physical volume rather than use a fixed amount of space for each file system.
• APFS supports sparse files, extended file attributes and TRIM operations, as well as using a copy-on-write metadata scheme to ensure that updates to the file system are crash-safe.
• Apple File System supports encryption natively, both single key encryption and multi-key encryption (where each file is encrypted with a separate key, and metadata is encrypted with a different key).

It is almost certain that any third party disc utilities will need to be updated. Once upgraded to APFS the only way to return to HFS+ is to erase the disc losing all data.

APFS implements normalization and case insensitivity according to the Unicode 9.0 standard; this enables APFS to support a wider range of languages for these features than HFS+, which is based on Unicode 3.2. However beta testers report issues with languages that include non-Roman characters. Hopefully this will be addressed soon.