Create space-saving clones on macOS with Python – alexwlchan

The standard Mac filesystem, APFS, has a feature called space-saving clones. This allows you to create multiple copies of a file without using additional disk space – the filesystem only stores a single copy of the data.

Although cloned files share data, they’re independent – you can edit one copy without affecting the other (unlike symlinks or hard links). APFS uses a technique called copy-on-write to store the data efficiently on disk – the cloned files continue to share any pieces they have in common.

Cloning files is both faster and uses less disk space than copying. If you’re working with large files – like photos, videos, or datasets – space-saving clones can be a big win.

For a recent project, I wanted to clone files using Python. There’s an open ticket to support file cloning in the Python standard library. In Python 3.14, there’s a new Path.copy() function which adds support for cloning on Linux – but there’s nothing yet for macOS.

Because the filesystem only has to keep one copy of the data, cloning a file doesn’t use more space on disk. We can see this with an experiment. Let’s start by creating a random file with 1GB of data, and checking our free disk size:

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