to change the usr directory in freebsd (i already make it)
add new hdd to your server, format it. let say i give the new patition is /usr2
after finish format
dump 0af - /usr | restore rf -
After the dump completed, edited /etc/fstab.
Delete the line with /usr in /etc/fstab.
Updated the line with /usr2, changed /usr2 for /usr. (inside fstab)
Then rebooted. Finally the system started with a new /usr filesystem.
Credit to BSD Forum!