Yet another cool Linux utility: tune2fs. When a partition is created on Linux it defaults to storing 5% of that partition for the super user (root). This was done to prevent the HD from ever filling up to 100% and preventing the system from booting up. On modern systems 5% is a HUGE chunk of drive space.

You can change this percent by issuing the following command:

tune2fs /dev/hda6 -mX Where X is the percentage you want to leave for the super user.