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Comment by yayoohooyahoo | Hacker News Reader

Is it not the same as a hard link (which I believe are supported on Mac too)?

My understanding is that it is a copy-on-write clone, not a hard link. [1]

> Q: Are clone files the same thing as symbolic links or hard links?

> A: No. Symbolic links ("symlinks") and hard links are ways to make two entries in the file system that share the same data. This might sound like the same thing as the space-saving clones used by Hyperspace, but there’s one important difference. With symlinks and hard links, a change to one of the files affects all the files.

> The space-saving clones made by Hyperspace are different. Changes to one clone file do not affect other files. Cloned files should look and behave exactly the same as they did before they were converted into clones.

[1] https://hypercritical.co/hyperspace/

What kind of changes could you make to one clone that would still qualify it as a clone? If there are changes, it's no longer the same file. Even after reading the How It Works[0] link, I'm not groking how it works. Is it making some sort of delta/diff that is applied to the original file? That's not possible for every file format like large media files. I could see that being interesting for text based files, but that gets complicated for complex files.

[0] https://hypercritical.co/hyperspace/#how-it-works

If I understand correctly, a COW clone references the same contents (just like a hardlink) as long as all the filesystem references are pointing to identical file contents.

Once you open one of the reference handles and modify the contents, the copy-on-write process is invoked by the filesystem, and the underlying data is copied into a new, separate file with your new changes, breaking the link.

Comparing with a hardlink, there is no copy-on-write, so any changes made to the contents when editing the file opened from one reference would also show up if you open the other hardlinks to the same file contents.

ah, that's where the copy-on-write takes place. sometimes, just reading it written by someone else is the knock upside the head I need.

That’s correct.

Almost, but the difference is that if you change one of hardlinked files, you change "all of them". (It's really the same file but with different paths.)

https://hypercritical.co/hyperspace/#how-it-works

APFS apparently allows for creating "link files" which when changed, start to diverge.

A copy-on-write clone is not the same thing as a hard link.

With a hard link, the content of each of the two 'files' are identical in perpetuity.

With APFS Clones, the contents start off identical, but can be changed independently. If you change a small part of a file, those block(s) will need to be created, but the existing blocks will continue to be shared with the clone.

It’s not the same because clones can have separate meta data; in addition, if a cloned file changes, it stores a diff of the changes from the original.

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