I have FreeBSD 8.2 installed on AMD/64 with 3 GB RAM and 690 GB pooled HD under ZFS. I have two copies of an identical file (180 MB video) in same directory and yet df -h indicates that both are using storage. I thought de-dupe was "built-in" with ZFS. Have I configured something wrong?
FreeBSD 8.2 only supports ZFS v15, but dedupe requires at least v21. Link
I think that dedupe is coming with FreeBSD 8.3.