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I’m trying to find a way to reliably convert Windows 10 installations from MBR (BIOS) to GPT (UEFI), but keep running into specific problems.

I recently installed a Samsung 980 M2 SSD on an older Asus H97-Pro motherboard. That PC had a MBR Win10 installation and provided a good opportunity to test said MBR to GPT conversion. Which, as you may have deduced by now, has not been going smoothly. My goal is to get the existing Win10 installation from an MBR sata-ssd to the GPT-formatted 980 and to turn off legacy support on the motherboard (=UEFI only).

I had to upgrade the mobo’s firmware to the most recent version (2906) to make the 980 show up in the BIOS.

I then turned the 980 into a blank MBR disk and copied all Windows partitions from the MBR sata SSD to the 980. (Afterwards, I disconnected the sata SSD.) Converting the 980 in that state from MBR to GPT fails:

  • Microsoft’s MBR2GPT fails to validate the drive.
  • Converting the MBR drive to GPT in Minitool Partition Wizard 11 (Windows PE) seemed to be more successful, until booting the result ended in a black screen containing only a Windows 10 mouse cursor with a small blue circle (loading animation) on top of it.

Efforts to repair that installation were unsuccessful:

  • I tried Macrium Reflect (Windows PE) > fix Windows boot problems, which completed without errors but didn’t solve the issue.
  • Boot Repair on a bootable Windows 10 installation thumb drive reported being unable to repair.

The last thing I tried was a fresh Windows installation on the 980, with the mobo set to UEFI only. This resulted in a bootable Windows installation. I then replaced the Windows partition (not touching the other two) with the Windows partition from the MBR installation. Windows booted into automatic repair, which once more reported being unable to repair after.

The exact version of Windows I’m trying to install, as well as that of the existing MBR installation, is Windows 10 Enterprise (N) LTSC 2019. This is in fact a 1809 build that receives updates. 1809 is an older base. Could it be lacking a specific driver for the 980? If so, what would be the most efficient way to add it to an existing installation? Personally I think it’s unlikely, as I have installed this Windows version on NVMe SSD’s before.

What am I missing here? I have been unable to find a solution to this problem in posts on this website as well as others. Mobo is currently set to UEFI only, secure boot disabled, AHCI mode, Intel Rapid Storage off.

Bart
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  • Post your current partition layout – Ramhound Aug 10 '21 at 00:24
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    With he time you already wasted with moving partitions and failed attempts of conversion you could have reinstalled Windows twice, at least. – ChanganAuto Aug 10 '21 at 00:34
  • does your current layout satisfy all the requirements in https://docs.microsoft.com/en-us/windows/deployment/mbr-to-gpt? [Cannot convert from MBR to GPT](https://superuser.com/q/1377951/241386) – phuclv Aug 10 '21 at 02:02
  • By performing an [edit] to your question, it can be reopened, but your [edit] must be substantial otherwise it will remain closed. – Ramhound Aug 10 '21 at 02:10
  • @ChanganAuto, I'm aware of that. Like I said, this is just a test case. I’ll be forced to upgrade a bunch of computers in the upcoming years, and the thought of fresh installs on all of them is not appealing. – Bart Aug 10 '21 at 08:13
  • @Ramhound, I had read that post, but was unable to solve my problem. I'll keep looking. – Bart Aug 10 '21 at 08:15
  • @phuclv, I actually gave up on MBR2GPT fairly quickly, as I assumed Minitool Partition Wizard would take care of those conditions for me. (I had picked up Minitool as a recommendation in the post which you later referred to.) But Minitool ultimately failed. (When the conversion starts, it warns about setting BIOS to UEFI in order to avoid boot issues. It then deletes and adds the necessary partitions and completes the conversion without errors. Afterwards, the disk shows as GPT. All as one would xpect. But ultimately, the result did not boot.) – Bart Aug 10 '21 at 09:56
  • I finally succeeded. Deleted all partitions from the target SSD and converted it to MBR, again. Copied the 3 Windows partitions from the MBR source (system reserved (boot), Windows, recovery) to the target. Last time, I tried using Minitool Partition Wizard at this point, which failed. I hadn't bothered with the MBR2GPT conditions, assuming Minitool would take care of those. This time, I made sure there was unallocated space before the first and after the last partition, made them primary, marked the first as active. Then I converted to GPT using AOMEI Partition Assistant, which did the trick. – Bart Aug 10 '21 at 09:57

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