[ale] HELP - Out of Storage on /

[JD]

20GB partition mounted on /.
df is reporting 100% used on /.
If I add up all the reported storage, only 4.7GB is used.


$ \df -k
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             19501440  19497112      4328 100% /
none                   4088752       348   4088404   1% /dev
none                   4093728         0   4093728   0% /dev/shm
none                   4093728       600   4093128   1% /var/run
none                   4093728         0   4093728   0% /var/lock
none                   4093728         0   4093728   0% /lib/init/rw

I can't figure out which files are using all the storage. I know this sounds
really dumb.  Removed the other physical partitions from the du -s listing.

$ sudo \du -sk
8072    /bin/
36644   /boot/
12980   /etc/
52      /home/
318052  /lib/
12460   /lib32/
58952   lost+found/
12      /mnt/
1156    /root/
10692   /sbin/
0       /sys/
16      /tmp/
3702072 /usr/
585264  /var/

It is an Ubuntu Server x64 10.04.3 (up to date patched) system mainly used for
file storage and running KVM VMs.

* Disabled ureadahead and rebooted this morning hoping that was the issue. It
wasn't.
* Forced an fsck and rebooted this morning. The numbers above are post-reboot.

Any ideas to find the disk sucking files?