Testing a USB Windows Install disk with Hyper-V

Recently I was putting together a new Windows USB Install disk (if you are not familiar with the process for doing this – here is a good article: http://windowsitpro.com/windows-8/q-how-do-i-create-bootable-usb-stick-can-install-uefi-system).  I really wanted to use virtual machines to test the disk as I was putting together (I am using unattended installation files and various scripts) however you cannot boot a Hyper-V virtual machine off of a USB key.

So what could I do?

The answer is surprisingly simple.  If you setup a virtual hard disk in exactly the same way that you do a USB install disk – you can use it to install Windows.

The process that I followed was to:

  1. Create a 32GB dynamic VHDX file using Hyper-V
  2. Mount the VHDX file in the host operating system – and then use DISKPART to create a FAT32 partition on it (that is marked as active), as discussed in the article above
  3. Copy in the Windows install files (and my custom scripts and tweaks)
  4. Create a virtual machine with this 32GB VHDX as the first hard disk, and a blank VHDX as the second hard disk
  5. Boot the virtual machine and install the operating system

This allowed me to quickly and easily test my install scripts.  Once I had everything working the way I wanted – I just had to copy my files to a physical USB key and go.