ZFS is there. Great! Thanks Pawel!
Now I wait a little bit until the first bugs are ironed out, and then I move all my stuff to it. The nice part: when you have 2 machines and everything you use is jailed, you just can do this without an “interruption of service” (or at least only with a very small one). Just move the jails to the other machine, replace the old FS with ZFS, and then move all jails back.