Salutare,
Gata, am rezolvat era destul de simplu...

editat /etc/fstab adaugat o linie de genul /dev/ad0s2 /cache ufs rw 2 2
/sbin/newfs -u /dev/ad0s2
mount /dev/ad0s2
rezultatul:
# df -h
Filesystem Size Used Avail Capacity Mounted on
/dev/ad0s1a 22G 265M 20G 1% /
devfs 1.0K 1.0K 0B 100% /dev
/dev/ad0s2 120G 2.2G 108G 2% /cache
devfs 1.0K 1.0K 0B 100% /var/dhcpd/dev
asta dupa 2 zile de mers

Succes si multe multumiri celor ce isi bat capul cu acest minunat proiect!!!