The following window will appear. Scroll down to see all the available fields. On the right of the window, a virtual disc is displayed, and on it used and free space, with different colors, as a pie-chart.
Notice that this dialog shows the type of the disc, if it is open (writable) and also the number of sessions written on the disc, with additional information about them, like the File System used.
A similar topic is Recoder Information.