I am impressed…. my gmirror array continued to work even after the drives were renamed from da20 and da24 to ada0 and ada1. This happened when I tried out the ahci(4) for my SATA drives.
It’s the type of thing I’m striving for soon in my ZFS array.
All this started when I wanted to find out about making my ZFS array more resilient. See http://docs.freebsd.org/cgi/getmsg.cgi?fetch=663685+0+current/freebsd-stable (which is the top level post of the above mentioned link).