Apple File System

Apple File System (APFS) is a proprietary drive format system that Apple introduced in macOS High Sierra (10.13) in 2017. It was also adopted in iOS 10.3, tvOS 10.2, and watchOS 3.2.

Features
APFS is designed to accommodate the use of solid-state drive storage across Apple's product line and address shortcomings of the long-used HFS Plus (Mac OS Extended) drive format, such as the 2040 date limit. .

Cloning
When files are copied within the same APFS volume, the file system will "clone" the data by making a reference to the original, instead of writing to additional drive space. Changes are written to the drive when one or both of the files modified. This uses drive space more efficiently and improves performance of copying files witin the same drive. The potential drawback is that file corruption caused by in the original file would affect all of the cloned files.

File system structure
APFS-formatted drives are partitioned into "containers" in which individual volumes are assigned specific roles. Volumes with preboot, recovery, and virtual memory (VM) roles are not mounted and remain hidden by default. Starting with macOS Catalina (10.15), volumes can be organized into "volume groups" where the bootable macOS system and data are kept in separate volumes and the system is kept locked by default. The purpose of this separation is to protect the macOS system from modification by hackers.

The following is the storage structure of APFS using a (GPT):
 * Containers
 * Hidden volumes
 * Preboot
 * Recovery
 * Virtual memory
 * Visible volumes
 * Volume groups (macOS Catalina and later)
 * System volume (locked by default)
 * Data volume

Articles

 * Is APFS doing its job? Big Sur edition by hoakley at The Eclectic Light Company (2021-03-01)