If you have been testing Windows 7 or Windows Server 2008 R2, you must have come across native VHD booting feature. This allows us to boot OS from VHD file residing on the hard drive. You don’t need a Hypervisor to boot from VHD. Windows 7 boot architecure changed a bit to accomodate this. In fact, Windows Server 2008 has the option to boot from a file. But that was with only WIM images.
In a previous post, I had written about how you can capture a VHD from OS media. There is also a simple script to generate the VHDs without any manual effort. Now, in this post, let us look at how we can use one such VHDs to multi-boot with existing OS on a physical server. The procedure is straight forward. You just need to add a BCD entry. To do this,
1. At a command-prompt, Run diskpart
2. Within Diskpart, select vdisk file=C:\<VHDNAME>.VHD
3. Attach Vdisk
4. Assign Letter=R (If not already assigned; diskpart usually picks up whatever you had assigned during creation)
6. At the command prompt, move to R:\Windows\System32 and run bcdboot.exe R:\Windows. This will add an entry to the BCD of exiting OS
7. Once again, open diskpart
8. Within diskpart, Select vdisk file=C:\<VHDNAME>.vhd
9. Detach vdisk
10. exit and reboot the system
At this point, when Boot Manager comes up, you should see an entry added at the top of the list. Select the top most entry and press enter. Windows OS will start configuring based on your hardware and after a reboot, you should be at the logon prompt.