Try this, although I'm not sure:
Go to System Prefs; Displays; and then when it says something like order of where they go, i don't remember the name
Maybe it's gather dispalys - but, whatever the case, once you get to a window with both monitors there, basically 2 screens, one empty and one empty with the bar on top, drag the bar to the left or right, where the 30" screen is.
might work.