I'm looking for a tool that would monitor disk usage over time. What I'm looking for is folders or files that grow unexpectedly over a short period of time. 

I use [du](http://linuxcommand.org/man_pages/du1.html) , [ncdu](http://dev.yorhel.nl/ncdu), [baobab](http://www.marzocca.net/linux/baobab/) (when X is available), [filelight](https://en.wikipedia.org/wiki/Filelight) and [agedu](http://www.chiark.greenend.org.uk/~sgtatham/agedu/) to assess the situation in realtime. 

Part of the problem is that when that data is absorbed by [backuppc](http://backuppc.sourceforge.net/) is is then "hardish" to remove it from there. And so we get bloated backups. 

What I'm looking for would be an alert system with some sort of diff over [du](http://linuxcommand.org/man_pages/du1.html) reports... on a daily or weekly basis. 

Extra features : do the same with databases (postgres mainly). Notify user on a multi-user system.