I have a mid-2011 Core i7 Macbook Pro that currently is dual-booting a File-Vault encrypted OS X Lion installation and an OS X Snow Leopard installation. Unfortunately I need to keep both of these on the internal drive which I believe prevents me making yet another partition for Windows 7 via Bootcamp because of some limitation on the number of partitions (though I could be wrong on this).
I only need to run Windows 7 natively (for gaming, etc) every once and a while and what I would ideally like to do is install Windows 7 onto an external USB or Firewire drive and boot/run Windows from the external drive when needed.
I have successfully installed Windows 7 by temporarily swapping my internal drive and for my "external" drive. After installation Windows boots fine while the drive is inside the laptop, but when I move it to an external USB enclosure it is not listed as a boot option either from the startup menu (holding down Option on boot) or from the 'Start-up Disk' System Preferences.
Is it possible to run Windows 7 from an external drive? If so how?