Recently I needed to identify where all the space was going on our server.

I initially used the Novell Remote Management volume inventory tool, but while this is useful for identifying users and large individual files, it does not help track down specific folders that may contain large numbers of medium size files (e.g. photos).

I have previously done folder level scanning with the Folder Size tab extension as it is quick and easy to get to, but it requires scanning every time you close the Properties dialogue, which can be very time consuming.

After looking around online I found a great free utility that displays the info in an easy to explore graphical view.
OverDisk scans the drive or folder (this took around 10 mins for a drive containing hundreds of home directories) and then you can save the data so it does not need to constantly rescan (unless you make changes to files).You can also have it only rescan a certain subfolder rather than the entire drive again.

It presents the information in a sorted colour coded pie chart, allowing you to easily see which folders and files are using the most space.

You can click on the folder and the pie chart will change to reflect that folder or click the middle of graph to go up a level. Right clicking on a folder gives you an easy option to Open or Explore in Explorer.

The program is very easy to use and allowed me to rapidly determine which areas were using space, and take appropriate action (move, archive, delete, leave, etc).