strange problem with disk space

["Valerio Pachera" <sirio81@gmail.com>]

tjener:/# df -h
Filesystem         Dimens. Usati Disp. Uso% Montato su
/dev/hda7              12G   12G  436M  97% /
tmpfs                 760M     0  760M   0% /lib/init/rw
udev                   10M   84K   10M   1% /dev
tmpfs                 760M     0  760M   0% /dev/shm
none                  760M   56K  760M   1% /tmp

The comand above shows that the root is full but I'm not using 12gb!
I'm using around 7 Gb: 3,2 for /opt, 3,4 for /usr, less than one for /var

tjener:/# du -sh *
3,7M    bin
44M     boot
0       cdrom
256K    dev
12M     etc
4,0K    home
4,0K    initrd
0       initrd.img
0       initrd.img.old
180M    lib
16K     lost+found
32K     media
28K     mnt
3,2G    opt
0       proc
56M     root
5,8M    sbin
66M     skole
4,0K    srv
0       sys
48K     tmp
3,4G    usr
741M    var
0       vmlinuz
0       vmlinuz.old


Any idea?
I'm using Terra at the moment.