Macbook Pro i7 run from one external thunderbolt start volume

Hi,

I just bought a new Macbook Pro i7 and i want to try to start from one external thunderbolt hard drive. I just inserted my Mac Pro volume into one WD Thunderbolt Duo hard drive case to run the volume but it seems like it does not work i only get one inaccessible sign on the boot screen. How can i make it start from one external thunderbolt hard drive ?

Thank you.