geli

# dd if=/dev/random bs=64 count=1 of=/root/ada1.key
# geli init -s 4096 -K ada1.key /dev/ada1
Enter new passphrase:
Reenter new passphrase: 

Metadata backup can be found in /var/backups/ada1.eli and
can be restored with the following command:

        # geli restore /var/backups/ada1.eli /dev/ada1

Unlock the encrypted volume
# geli attach -k ada1.key /dev/ada1

Fill the volume with random data
# pv -ptre /dev/random | dd bs=1M of=/dev/ada1.eli

Format the new volume as UFS2
# newfs -L private /dev/ada1.eli

Unmount and detach encrypted volume
# umount /private
# geli detach ada1.eli