changing a zfs pool to another machine

Hi...

I have a zfs pool with 3 harddrives (ad8,ad10,ad15)

I need to change to another machine...

when I try to boot freebsd in the another machine with this 3 harddrives...
goes to mountroot prompt.

so.. I need to boot with

set vfs.root.mountfrom="zfs:tank/root"

but don't work... goes ever to mountroot prompt..