> Can you show us how an fsck would discover this bug but ZFS could never?

I'd have to read closer to be certain, but if my understanding of it is correct, you'd have orphaned objects in the file system. The orphaned objects would be detectable, but would have correct hashes.

Here's a better example of one where scrub clearly doesn't catch it, but fsck would (and zdb does). The metaslab structure could be checked in theory, but isn't. https://neurrone.com/posts/openzfs-silent-metaslab-corruptio...

> if so, wouldn't this just be a bug, like (a bug in) fsck, not some fundamental limitation of the system?

It's not a bug or a fundamental limitation of the system, it's just that fsck != scrub, and nobody has written the code for fsck. If someone wanted to write the code, they could. I suspect it wouldn't even be particularly hard.

But fsck != scrub, and they catch different things.