To repartition disk drive /duplicate file system in FreeBSD :
1. create new slice using bsdlabel
2. newfs newly created slice
3. mount it to /mnt (or wherever)
4. cd /mnt (or wherever)
5. try to minimize amount of the open files on source filesystem by killing all unnecessary daemons
6. dump -0ab 128 -C 32 -f - /dev/slicename | restore -rb 128 -f -
7. ensure backup is adequate
8. modify /etc/fstab and point new filesystem to desired mount point
9. check is everything ok throughly.
10 umount old mount point && mount new one or reboot if the live fs like e.g. /usr