How to use eject button on keyboard to eject external drive
So I have a Mac Pro 3,1 (Early 2008) and decided to use an external disc drive for convenience, but I have a problem: Keyboard eject button does not control it. Basically I want to switch (if possible) from it ejecting internal disc drive to controlling my external. Any help would be appreciated, as this is bothering me.
Mac Pro, OS X Yosemite (10.10.1)