under ubuntu the default disk analyser (baobab) don’t offer ignore directories option. In the case of we would like analyse the root folder / and ignore mounts in /media for example the easy way is to :

• create new temporary folder,
• mount the root filesystem on it,
• analyse the temporary folder
• unmount and delete it

So, first proceed like following

> sudo mkdir tmpAnalysis > sudo mount /dev/sda1 tmpAnalysis > baobab tmpAnalysis

Analysis is ready to explore. Then

> sudo umount tmpAnalysis > sudo rm -rf tmpAnalysis