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We are looking into Azure Site Recovery as a possible BCDR solution, and have encountered a bit of an issue in that Azure doesn't support UEFI firmware when synchronizing VMWare VMs.

Is there any way to convert from EFI firmware to Legacy without reinstalling the OS? I've read solutions to do the opposite, but no such luck with this scenario.

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This is, in fact, possible:

  1. Boot the system using a linux live cd with gdisk on it. I used a CentOS 7 Core installation and used recovery mode. I did this by editing the grub boot options and tacking on rescue to the end.
  2. Run gdisk on the disk with Windows installed. See the gdisk docs for more info.
  3. Reboot the machine into a Windows installation disk, and open up the command prompt using the repair your computer option.

At this point, I had to load the VMWare PVSCSI drivers, and already had the floppy with the drivers mounted. To do this, you can run drvload A:\AMD64\PVSCSI.INI. Alternatively, you can go through the initial Windows setup, and load the drivers via the GUI. You may then back out and click the Repair your computer link.

  1. Run the following commands to (with luck) restore the boot loader:

    bootrec.exe /FixMbr
    bootrec.exe /RebuildBcd
    

Note that your mileage may vary, and I would definitely at least snapshot the VM before doing this, but a full backup is better.

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3

Unfortunately you will need to reinstall after changing from uefi to legacy

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