I'm trying to identify why, suddenly, 100% of our disk space is in use. I have already rebooted but the issue persists.

Here are the outputs of some commands that are showing some strange (for me) results:

danny@hydrogen:~$ df -h

Filesystem            Size  Used Avail Use% Mounted on
/dev/cciss/c0d0p1     130G  122G  949M 100% /
none                  1.9G  196K  1.9G   1% /dev
none                  2.0G     0  2.0G   0% /dev/shm
none                  2.0G   40K  2.0G   1% /var/run
none                  2.0G     0  2.0G   0% /var/lock
none                  2.0G     0  2.0G   0% /lib/init/rw

danny@hydrogen:/$ sudo du -chs /

du: cannot access `/proc/1662/task/1662/fd/4': No such file or directory
du: cannot access `/proc/1662/task/1662/fdinfo/4': No such file or directory
du: cannot access `/proc/1662/fd/4': No such file or directory
du: cannot access `/proc/1662/fdinfo/4': No such file or directory

danny@hydrogen:/$ df

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/cciss/c0d0p1    135342296 128144108    323104 100% /
none                   1991336       196   1991140   1% /dev
none                   1995788         0   1995788   0% /dev/shm
none                   1995788        40   1995748   1% /var/run
none                   1995788         0   1995788   0% /var/lock
none                   1995788         0   1995788   0% /lib/init/rw

danny@hydrogen:/$ mount

/dev/cciss/c0d0p1 on / type ext4 (rw,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)

danny@hydrogen:/$ sudo du -h --max-depth=1

634M    ./premvet_sync
5.6M    ./etc
4.0K    ./opt
16K ./lost+found
7.4M    ./bin
623M    ./lib
196K    ./dev
0   ./sys
4.0K    ./srv
4.0K    ./cdrom
8.0K    ./media
52K ./tmp
... it hangs for ages here.....

The server is running Ubuntu 10.04.4 LTS.

System load:  2.85                Temperature:         8 C
Usage of /:   94.7% of 129.07GB   Processes:           132
Memory usage: 39%                 Users logged in:     0
Swap usage:   0%                  IP address for eth0: 192.168.1.124

=> / is using 94.7% of 129.07GB

I'm struggling to comprehend why this is happening! Any pointers would be appreciated.