My interest in file systems started when I discovered how type and creator codes1 and resource forks contributed to the fantastic user interface on my original Macintosh in 1984. In the late 1990s, when it looked like Apple might buy Be Inc. to solve its operating system problems, the Be File System was the part I was most excited about. When Apple bought NeXT instead and (eventually) created Mac OS X, I was extremely enthusiastic about the possibility of ZFS becoming the new file system for the Mac. But that didn’t happen either.
Finally, at WWDC 2017, Apple announced Apple File System (APFS) for macOS (after secretly test-converting everyone’s iPhones to APFS and then reverting them back to HFS+ as part of an earlier iOS 10.x update in one of the most audacious technological gambits in history).
APFS wasn’t ZFS, but it was still a huge leap over HFS+. Two of its most important features are point-in-time snapshots and copy-on-write clones. Snapshots allow for more reliable and efficient Time Machine backups. Copy-on-write clones are based on the same underlying architectural features that enable snapshots: a flexible arrangement between directory entries and their corresponding file contents.
Today, most Mac users don’t even notice that using the “Duplicate” command in the Finder to make a copy of a file doesn’t actually copy the file’s contents. Instead, it makes a “clone” file that shares its data with the original file. That’s why duplicating a file in the Finder is nearly instant, no matter how large the file is.