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GPT to MBR conversion without losing data (UEFI / Legacy BIOS switch)

by on Jan.14, 2014, under Computer Stuff

Changed ESXi virtual machine from UEFI to BIOS mode, so that bios440.rom trick can be used for SLIC.

Instructions copied from http://www.firewing1.com/node/610#gpttombr

The actual GPT to MBR conversion

Through the Rod Smith’s guidance and a few dirty tricks, I was successfully able to convert my GPT partition – without data loss or deleting any partitions – and then boot Windows 7 in legacy/MBR mode. In order to do this you’ll need your Windows installation media at hand as well as a copy of the Fedora 16 Live media. If you don’t have a copy of Fedora 16 Live handy, you can download the Live media ISO (64-bit) from a local mirror here

 Keep in mind that at this point I only had 3 partitions and a bunch of unpartitioned space on the disk, so conversion was a rather straightforward process (all GPT partitions mapped directly to primary partitions). Although it is theoretically possible to convert GPT partitions with >4 partitions by defining which ones are to be logical partitions after conversion, I have not tested this.
  1. Boot your Fedora 16 Live media and wait for your session to start. If you’re having troubles booting, press Tab at the boot loader screen and try booting with the nomodeset parameter added.
  2. Depending on your graphics card, you’ll either be presented with the new Gnome 3 Shell or with the traditional interface. Start a terminal session by putting your mouse in the top right corner of the screen and typing “terminal” in the search (Gnome Shell) or by selecting Applications > System Tools > Terminal (traditional interface)
  3. Install gdisk:
    su -
    yum -y install gdisk

    This may take a few moments.

  4. Make a backup of your current GPT scheme:
    gdisk -b sda-preconvert.gpt /dev/sda
  5. Now we will attempt to convert your GPT disk layout to MS-DOS/MBR. Start gdisk:
    gdisk /dev/sda

    You should be prompted with:

    Command (? for help):
  6. Press r to start recovery/transformation.
  7. Press g to convert GPT to MBR.
  8. Press p to preview the converted MBR partition table.
  9. Make any modification necessary to the partition layout. See Rod Smith’s Converting to or from GPT
    External Links icon

    page for more details on this.

  10. When you’re happy with the MS-DOS/MBR layout, press w to write changes to the disk.
  11. Shutdown Fedora 16 and boot from the Windows 7 installation media
  12. Enter your language & keyboard layout and then select the option to repair your computer in the bottom left corner.
  13. From the available options, select Startup Repair. Windows will ask for a reboot.
  14. Follow the previous three steps again to boot the Windows 7 installation and run startup repair
  15. Once again, boot the Windows 7 installation media but this time opt to open a command prompt instead of choosing startup repair. Type:
    bootrec /scanos
    bootrec /rebuildbcd
    bootrec /fixmbr
    bootrec /fixboot
  16. Close the command prompt and run Startup Repair one last time.

That’s it! You should now have a bootable installation of Windows 7 on a MBR partition layout.


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