Quoting "Austin S. Hemmelgarn" <ahferro...@gmail.com>:
Defrag may break up extents. Defrag may fuse extents. But it
shouln't ever unshare extents.
Actually, spitting or merging extents will unshare them in a large
majority of cases.
Ok, this point seems to be repeated over and over without any proof,
and it is illogical to me.
About merging extents: a defrag should merge extents ONLY when both
extents are shared by the same files (and when those extents are
neighbours in both files). In other words, defrag should always merge
without unsharing. Let's call that operation "fusing extents", so that
there are no more misunderstandings.
=== I CHALLENGE you and anyone else on this mailing list: ===
- Show me an exaple where splitting an extent requires unsharing,
and this split is needed to defrag.
Make it clear, write it yourself, I don't want any machine-made outputs.
