Microsoft does not support booting Windows from external drives
If you do decide to install Windows to a USB drive, a Flash Drive(UFD) drive, ESATA drive or store Windows Native Boot VHD on USB/UFD drive, it will not be supported by Microsoft. The reasons why this is not supported have been mentioned in KB2485453: However, there are some specialized products that support this type of scenario, viz., installation on external drives :
Windows Embedded supports this scenarioMicrosoft Hyper-V Server supports the ability to boot from a USB flash device (UFD). Booting Hyper-V Server from a USB flash drive is only supported for OEMs.
Just so you know.
