I have a ZFS filesystems which has been running for some time and I recently had the opportunity to upgrade it (finally!) to the latest ZSF version. Our data doesn't scream dedup but I firmly believe based on small tests that we could gain anywhere from 5-10% of our space back for free by utilizing it. I have enabled dedup on the filesystem and new files are slowly being dedupified but the majority (95%+) of our data already exists on the filesystem.

Short of moving the data off-pool and then recopying it back, is there any way to trigger a dedup scan of existing data? It doesn't have to be asynchronous or live.

(And FYI there isn't enough room on the pool to copy the entire filesystem to another and then just switch the mounts.)