How to bring a Time Machine backup to its knees: get it to back up a sparse file to an HFS+ disk. It’ll take forever and run you out of free space.
sparse file
Looking in more detail at newer tricks used by APFS on the data of files: sparse files, which can squeeze vast empty files almost to nothing; file clones; and compression, opening up in Big Sur.
Now shows the space taken on disk, which makes it easy to identify sparse files.
An ingenious idea to save storage space: leave out empty areas in large files – make them sparse. Do they exist in APFS as claimed?
Why measuring free and used disk space is not so simple in APFS, and which estimates you should trust.
Does APFS support its major new features – clones, snapshots, etc – yet, and how can you use them?
The Eclectic Light Company 