Running Ubuntu 10.04 and nearly all my drive space is gone.

# df -h
Filesystem            Size Used Avail Use% Mounted on
/dev/mapper/ubuntu-root
                      7.3G  6.6G  327M  96% /
none                  245M  240K  244M   1% /dev
none                  249M     0  249M   0% /dev/shm
none                  249M  340K  249M   1% /var/run
none                  249M     0  249M   0% /var/lock
none                  249M     0  249M   0% /lib/init/rw
/dev/sda1             228M   34M  183M  16% /boot

Of course it's not mounted. I read that chmod 0 /sbin/debugfs could fix the problem, but now it just won't mount despite changing the permission to 777. This is a VM running on VirtualBox. I have done a file system check which ran fine.

What is this directory and how can I remove it from the system?