How would this work if I have snapshots? Wouldn’t then the version of the file I just replaced still be in use there? But maybe I also need to store the copy again if I make another snapshot because the “original “ file isn’t part of the snapshot? So now I’m effectively storing more not less?
AFAIK, yes. Blocks are reference counted, so if the duplicate file is in a snapshot then the blocks would be referenced by the snapshot and hence not be eligible for deallocation. Only once the reference count falls to zero would the block be freed.
This is par for the course with ZFS though. If you delete a non-duplicated file you don't get the space back until any snapshots referencing the file are deleted.
Yes that snapshots incur a cost I know. But I’m wondering whether now the action of deduplicating actually created an extra copy instead of saving’one.
