I wanna install Ubuntu on my external usb hard drive. I want that Ubuntu only boots if my second drive is plugged in and that windows boots if my second hard drive isn't plugged in. I already had ubuntu installed but then Ubuntu and Windows only booted if my second drive was plugged in. That means I had to plug in my second hard drive every time I wanted to start windows or ubuntu. I fixed this problem, but now I have to reinstall ubuntu and i want it that ubuntu boots only with my second drive plugged in and that windows boots if my second drive isn't plugged in. Can someone help me?