https://www.theictguy.co.uk/disk2vhd-hyper-v-boot-failure-with-gen2-server/
Had an issue with a P2V of a Dell T330 with Windows Server 2012 R2 installed today. The Disk2VHD creation went fine and completed successfully. The VHDX files were moved to the new Hyper-V host and added to a Gen 2 VM, the problem occurred when booting.
Hyper-V unable to boot due to 99Mb RAW volume. disk2vhd Hyper-V boot failure.
- Add a new DVD Drive to the VM and mount the ISO for the Server OS you are trying to boot
- Change the boot order of the server to boot from DVD
- Turn on the server and when requested press any key to continue
- When the install has booted click Repair your computer
- Click Troubleshoot
- Click Command Prompt
- Type disk part
- Type list disk
- Type select disk 0 (or your main system disk)
- Type list volume and note which volume is showing as 99MB RAW
- Type select volume 3 (or whatever volume is your 99Mb RAW volume)
- Type assign letter L:
- Type FORMAT FS=FAT32 LABEL=”BOOT”
- Change to the new disk, type L:
- Type bootrec /fixboot to create the new boot record
- Type bcdboot C:\Windows /l en-us /s l: /f ALL to create a new BCD Store and to copy over the boot files from the Windows directory of the existing installation you are trying to boot.
- Type exit
- Click Continue to boot into your server as normal
- It is normal for the server to take longer to boot due to new hardware being detected and installed
- You may need to set the IP Address of the server on the NIC as it often installed a new Hyper-V NIC and doesn’t copy the original settings over.