[rappatic]

I wondered that too.

If we only have two files, A and its duplicate B with some changes as a diff, this works pretty well. Even if the user deletes A, the OS could just apply the diff to the file on disk, unlink A, and assign B to that file.

But if we have A and two different diffs B1 and B2, then try to delete A, it gets a little murkier. Either you do the above process and recalculate the diff for B2 to make it a diff of B1; or you keep the original A floating around on disk, not linked to any file.

Similarly, if you try to modify A, you'd need to recalculate the diffs for all the duplicates. Alternatively, you could do version tracking and have the duplicate's diffs be on a specific version of A. Then every file would have a chain of diffs stretching back to the original content of the file. Complex but could be useful.

It's certainly an interesting concept but might be more trouble than it's worth.

[abrookewood]

ZFS does this by de-duplicating at the block level, not the file level. It means you can do what you want without needing to keep track of a chain of differences between files. Note that de-duplication on ZFS has had issues in the past, so there is definitely a trade-off. A newer version of de-duplication sounds interesting, but I don't have any experience with it: https://www.truenas.com/docs/references/zfsdeduplication/