• Changing from MBR to GPT

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    I’m running W10 and W7 on a dual boot setup, each OS is on a seperate SSD and data is on several HDD’s, the whole system is MBR. I now have a 4Tb drive and want to change my system from MBR to GPT so I can use the capacity.
    I have an ASUS P8Z68-V/Gen3 motherboard, which I believe can run as EUFI, but I don’t know where to start to make the conversion.
    Any advice would be greatly appreciated.

    Viewing 9 reply threads
    • #2302533

      I think we need to see your disk configuration to advise.
      Open “Disk Management” and expand it to show all the disk information, then take a screenshot, save as PNG and attach here.

      cheers, Paul

      p.s. Use Windows Snipping Tool / Snip n Sketch for the screenshot.

    • #2302622

      It can get complicated.  MBR and GPT have incompatible disk and partition addressing.  You also need an EFI partition because Windows can’t boot directly from GPT.

      Here’s how I did it with my laptop a little over 7 years ago:  Adventures with UEFI and Backing into a dual boot in UEFI. Read through both of those threads; there are several posts with pertinent information.

      I strongly advise creating full drive images of all your drives before starting.

      Always create a fresh drive image before making system changes/Windows updates; you may need to start over!
      We were all once "Average Users". We all have our own reasons for doing the things that we do with our systems, we don't need anyone's approval, and we don't all have to do the same things.

      • This reply was modified 2 years, 11 months ago by bbearren. Reason: clarity
    • #2302752

      I now have a 4Tb drive and want to change my system from MBR to GPT so I can use the capacity.

      If you’re not switching boot (“C:”) to the new drive, you don’t have to do anything to your old drives.

      Windows Vista or later booted from MBR is able to use secondary GPT drives just fine for non-boot data, see https://docs.microsoft.com/en-us/troubleshoot/windows-server/backup-and-storage/support-for-hard-disks-exceeding-2-tb table 4, and a bit further down instructions on how to partition your data disk.

      Even systems without UEFI and therefore unable to boot from GPT on Windows can use large disks for data this way. (One of my sons has such a thing.)

      You only need to do the conversion if you want to boot from the new drive and use its full capacity.

    • #2302808

      PaulT see attached screen shot. Drive 0 is the 4Tb drive.


      mn- This looks interesting, but do I have to lose all content when carrying out the conversion.


    • #2302855

      do I have to lose all content when carrying out the conversion.

      I have used Mini Tool Partition Wizard (Free version) many times to change an MBR drive to GPT without any data loss.  It will also similarly change GPT to MBR.

      Look here for it: https://www.partitionwizard.com/

      At the site, choose the drop-down for “Home user”.

      Memory is that during install it also asks if you want to install something called “Volume Shadow Copy Service”.  It works OK for your purposes to NOT select this feature.

      As well, in one of the later screens it may offer you some version of Norton or McAfee protection and this can also be “declined”.

      1 user thanked author for this post.
    • #2303004

      Ouch! What a mass of disks.

      It looks like you use MBR to boot from disk 1 (W7) and it offers W7 from disk 1 or W10 from Disk 3. This has the potential to be very hard to repair is you lose a disk because MBR boot is disk location specific.

      To confirm this assumption we need some details from your system.
      In both W7 and W10.
      Win R, msinfo32, Enter
      We need the “BIOS Mode” and “Boot Device” information. See attached screenshot.

      cheers, Paul




    • #2303069

      Here’s my msinfo32 data;

      W10 BIOS Mode Legacy
      W10 Boot Device \Device\HarddiskVolume2
      W7 Boot Device \Device\HarddiskVolume2

      There’s no entry for BIOS Mode in W7

      I use Easy BCD to set up boot options, here’s the details page for both windows versions, in case it helps

      EasyBCD W10

      Default: Windows 10
      Timeout: 10 seconds
      EasyBCD Boot Device: C:\

      Entry #1
      Name: Windows 10
      BCD ID: {current}
      Drive: C:\
      Bootloader Path: \WINDOWS\system32\winload.exe

      Entry #2
      Name: Windows 7
      BCD ID: {0c468363-eb83-11e4-a44b-eb5e6d3b2ea1}
      Device: boot
      Bootloader Path: \Windows\system32\winload.exe

      EasyBCD W7

      Default: Windows 10
      Timeout: 10 seconds
      EasyBCD Boot Device: C:\

      Entry #1
      Name: Windows 10
      BCD ID: {default}
      Device: \Device\HarddiskVolume4
      Bootloader Path: \WINDOWS\system32\winload.exe

      Entry #2
      Name: Windows 7
      BCD ID: {current}
      Device: boot
      Bootloader Path: \Windows\system32\winload.exe

      I have used Mini Tool Partition Wizard (thanks Al Taylor) to successfully convert my 4Tb drive to GPT, but I’m still interested in converting the system to UEFI.



    • #2303084

      I’m still interested in converting the system to UEFI.


      This is, theoretically, well supported on Windows 10, in a single boot / single disk configuration, and assuming no problems on the firmware side. Converting 64-bit Windows 7 is not officially supported by Microsoft but known to usually work with the right tools. (32-bit 7 is known to not do UEFI.)

      Asus doesn’t really have release notes for the firmware releases but I note that the latest version is from 2012 … and at that time UEFI bugs were still very common.

      And I really wouldn’t be all that surprised if your multiboot or the menu would need some manual fixing to work right after the conversion.

      Conversion itself is fairly simple if you’re using one of the tools intended for this, and specific steps would depend on the tool. Though one thing I’d note that there’s a bit of a chicken-and-egg problem with the UEFI boot settings, because usually those cannot be accessed while in BIOS mode… so might have to reboot several times.

      The same MiniTool Partition Wizard you already used should have a converter function.

      Aomei Partition Assistant Pro has been recommended by some.

      I wouldn’t know if gptgen is better or worse than Microsoft’s official mbr2gpt.

      And, Microsoft’s mbr2gpt utility is known to have issues if the disk configuration is something other than it expects – things like “System Reserved Partition” being on a different physical device than C:. So, might possibly have to do other things first before that’ll work…

    • #2303223

      You have 2 options.
      1. Leave well enough alone.
      2. Go for it. This is the best and most difficult option.

      Changing the boot mode

      Make sure you have a computer you can use to pop in and ask questions when yours is not working. Alternatively, make a Linux Live USB to boot the non working machine so you can use the internet.

      1. Make an image backup of the W7 and W10 disks.
      2. Create a W10 recovery USB.
      3. Disconnect the W7 disk – no need to muck it up.
      4. Use MiniTool PW to convert disk 3 (W10) to GPT and add a 100MB FAT32 partition to the front.
      5. Boot into the BIOS and change to UEFI boot. Reboot to confirm a non-bootable system.
      6. Boot the recovery USB and select repair and automatic. Hopefully this will copy the boot files to your new 100MB partition. If not, follow the manual method on this page to copy the files.

      If you can’t persuade the Windows boot disk to do what you want, try the Paragon Software recovery product (free for home use).

      Once you have W10 in EFI mode you should be able to reconnect the W7 disk and convert it to EFI.

      cheers, Paul

    • #2303234

      Thanks guys for all the info.
      Having successfully changed the new data drive to GPT I think I’ll stick with MBR for the operating systems for now. I may be into a new motherboard and cpu next year, when I’ll drop W7. In that case I can introduce EUFI then.


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