Resolved Boot MBA from USB3 drive

Hi,

I have a summer 2012 Macbook Air for my job. I want to be able to use it as my private laptop as well, to replace my early 2008 Macbook Pro.
The internal ssd of the MBA has not enough space for my personal apps, and replacing it with a bigger one is not allowed by my boss (and neither is putting all my own apps and stuff on it).

I bought a Samsung 840pro 256GB SSD, and installed in a Thermaltake Silver River 5G USB3 enclosure. I am able to install Mountain Lion using the recovery option when booting the MBA. Unfortunately, I'm not able to boot from the external disk. When I boot holding 'alt', the disk does not show up...

Has anybody any experience with booting a Macbook Air from an external usb3 ssd?

Thanks for your help!

Rik

Problem solved

I did it!

I could not clone the internal drive, because it's encrypted and all my work stuff is on there.
I started the install using recovery mode in the MBA, and then I connected the disk to my Macbook Pro, which wanted to boot it (maybe because it's usb2), and finished the installation there.
Now I am able to boot the MBA from the external drive.

Thank you for your reply Weaselboy.