FreeBSD gmirror raid 1 setup

After installing the system on disk ad0, and wanting it to be mirrored at disk ad1.

Eventually see:
http://www.freebsd.org/doc/en/books/handbook/geom-mirror.html

sysctl kern.geom.debugflags=17
gmirror label -vb round-robin gm0 /dev/ad0
gmirror load
echo 'geom_mirror_load="YES"' >> /boot/loader.conf
cp /etc/fstab /etc/fstab.old

# vi /etc/fstab
Replace all old ad0 references with mirror/gm0 by typing :%s/ad/mirror\/gm/g.

reboot

gmirror insert gm0 /dev/ad1
gmirror status

The mirror is being build, which takes a while. Check with gmirror status..