We'd like to implement something similar to the "baobab" tool on Ubuntu. It's a tool that displays information about the size of all the folders and files in the hard drive.
It starts with a simple donut chart representing the aggregated size of the top-level folders. Then if one is interested, one can click on a given top-level folder, which leads to a new donut chart showing in detail the sizes of each subfolder inside that top-level folder.
Also, the drilldown will bring me to the same dashboard, regardless of where in the pie chart I click.
Let's say I have 2 categories in the pie chart, with 60-40 split. If I click on the item with 60%, I want to go deeper into that 60%, whereas if I click on the 40% item, I want to go deeper only in that one.