Question WIndows 11 hardware support question, changing an existing SSD with partitions from MBR partition style to GPT partition style

William Gaatjes · Apr 18, 2025

Hi all, i have a computer that is capable of being windows11 compliant.

Of course, there is a caveat :
The only thing i have to do with a new fresh install, is convert the SSD form MBR to GPT. And disable in the bios the CSM module.
This to get the UEFI part of the bios to run with secure boot.

Is the program MBR2GPT.exe also present on the install USB stick that is created with the media creation tool ?

Can i just start with the cmd commandline using the install usb stick ?

Steps to take :

1 Erase all data on the ssd , remove the partitions.
2 convert the SSD from MBR to GPT through MBR2GPT.exe.
3 Then disable in the bios the CSM module.
4 Start again with the install usb stick
5 Install windows 11.

It has been a while with me installing windows.

kn51 · Apr 18, 2025

Starting fresh? Set bios to uefi, nuke partitions during setup.

MBR2GPT will convert current MBR installs to GPT. Which then you have to flip to uefi half-way through. (Useful if doing an upgrade, but sounds like you are doing a clean install)

William Gaatjes · Apr 19, 2025

I see. Thank you.
Yes, i will be doing a fresh install, because of the MBR/GPT issue.
Making backups, remove partitions , converting MBR to GPT , restoring partitions and and writing the backups back is too much work.
My data disk is GPT already.
My main windows disk is MBR.

But i remember that in the past windows 10 would not install with some X80xxxxx error code and after converting my ssd to MBR , windows would install.
I did not know at the time that in my BIOS the CSM module was active and therefore UEFI was inactive and therefore installing W10 at the time on a GPT disk would fail and W10 setup came up with an X800xxxxx error code.
I just googled for the solution at the time and converting to MBR was written down as a solution at the microsoft support sites. It was not mentioned that UEFI needs to be active and CSM to be inactive, and that is the first option to be checked before converting the install disk to MBR.

Now, W11 needs GPT and i am having the same issue.

I do not know how the W11 setup progresses. I have never used it.

And i am very dependent on my computers at the moment.
I need to have the computer up and running within a few hours on the same day.

I am making a schedule with a list of tasks like making backups to make sure that i do not mis anything.

After that i will try using rufus + windows 11 on another pc .

tecknot · Apr 23, 2025

Hi William,

You can convert an MBR disk to a GPT disk simply by going into Diskpart (type in "Diskpart" at the prompt) in a command prompt (as administrator). Now type in "list disk," and select the desired disk by typing "select disk #" (just exchange the "#" with the desired disk number). Type in "clean" to delete all items and partitions from the disk. From there you can just type "convert GPT" and that will do it. Now you just create the desired partitions and format. (Let me know if you need instructions for Diskpart.) See screenshots attached.

Kind regards,

tecknot

William Gaatjes · Apr 28, 2025

tecknot said:
Hi William,

You can convert an MBR disk to a GPT disk simply by going into Diskpart (type in "Diskpart" at the prompt) in a command prompt (as administrator). Now type in "list disk," and select the desired disk by typing "select disk #" (just exchange the "#" with the desired disk number). Type in "clean" to delete all items and partitions from the disk. From there you can just type "convert GPT" and that will do it. Now you just create the desired partitions and format. (Let me know if you need instructions for Diskpart.) See screenshots attached.

Kind regards,

tecknot

Hi,

That is an option that is not possible for me. Because it is my main SSD where windows is installed upon.
And all options are greyed out even when logged in as admin.

Best is to boot from W11install USB stick,
I will do a fresh install , disable CSM to enable UEFI booting. And remove all partitions then on my SSD and convert to GPT with diskpart, list disk, clean , convert GPT.
Then fresh install W11.

I have only 3 partitions on my SSD and it seems MBR2GPT.exe can handle that while W10 is running. But it is strongly recommended to make backups.
Because sometimes MBT to GPT conversion with MBR2GPT does not work.
And the only solution then is either restore from backup or a fresh install.

William Gaatjes · Apr 28, 2025

tecknot said:
Hi William,

You can convert an MBR disk to a GPT disk simply by going into Diskpart (type in "Diskpart" at the prompt) in a command prompt (as administrator). Now type in "list disk," and select the desired disk by typing "select disk #" (just exchange the "#" with the desired disk number). Type in "clean" to delete all items and partitions from the disk. From there you can just type "convert GPT" and that will do it. Now you just create the desired partitions and format. (Let me know if you need instructions for Diskpart.) See screenshots attached.

Kind regards,

tecknot

Hi tecknot

I think i know where it went wrong in the past when i installed W10.

My HDD is 500GB and my SSD is also 500GB.
My HDD is labeled as DISK 0 and my SSD is labeled as DISK 1.

My HDD is converted to GPT.
My SSD is not converted to GPT and is MBR.

i also see this when i do the diskpart command ; list disk.

That is where i learned that it is a good idea to physically disconnect the PCIe connector from my 500 GB HDD for a moment during windows installation. Of course the PCB is turned off when i disconnect the PCIe connector.
So that the 500GB SDD becomes DISK 0 and is for a moment the only disk.

i remember long ago when i installed W10 on my then at the time new system, i almost made a mistake with assuming that DISK 0 is the SSD.

Regards, William.

bba-tcg · Apr 28, 2025

William Gaatjes said:
Hi,

That is an option that is not possible for me. Because it is my main SSD where windows is installed upon.
And all options are greyed out even when logged in as admin.

Best is to boot from W11install USB stick,
I will do a fresh install , disable CSM to enable UEFI booting. And remove all partitions then on my SSD and convert to GPT with diskpart, list disk, clean , convert GPT.
Then fresh install W11.

I have only 3 partitions on my SSD and it seems MBR2GPT.exe can handle that while W10 is running. But it is strongly recommended to make backups.
Because sometimes MBT to GPT conversion with MBR2GPT does not work.
And the only solution then is either restore from backup or a fresh install.

Which you plan to do anyway, apparently. So what's the harm in trying mbr2gpt.exe first?

William Gaatjes · Apr 29, 2025

bba-tcg said:
Which you plan to do anyway, apparently. So what's the harm in trying mbr2gpt.exe first?

First i need to prepare. Making a backup from everything that is important.
And i need to have the time for it. That i have enough time to solve problems.
Then i can try to convert my SSD from MBR to GPT.
I have to inform myself first about what i am going to have to do.

mikeymikec · Apr 29, 2025

I've used mbr2gpt a few times. You can even run it from within the live Windows of that Windows installation (there's a documented command switch that can do it).

After that's done, make the BIOS change and boot back into Windows.

Windows could then do an in-place upgrade for you.

bba-tcg · Apr 29, 2025

William Gaatjes said:
First i need to prepare. Making a backup from everything that is important.
And i need to have the time for it. That i have enough time to solve problems.
Then i can try to convert my SSD from MBR to GPT.
I have to inform myself first about what i am going to have to do.

Sure. I've never had mbr2gpt.exe mangle anything. I've had it fail a time or two, but when it did, everything was as it had been previously. But caution is always good. I'm just saying I would try it before going to the trouble of a clean install unless you just want a clean install. But even then, if you change the boot mode in the UEFI to UEFI before booting from the flash drive, all you have to do is delete all the partitions on the target drive and when you select that drive for installation, Windows will make the drive GPT. No need for all the steps in your original post if doing a clean install.

And I agree about disconnecting any other drives before doing a clean install.

mikeymikec · Apr 30, 2025

bba-tcg said:
And I agree about disconnecting any other drives before doing a clean install.

Me too, though I wonder if Windows setup can actually handle multiple drives in a decent manner now, it might be one of those sufficiently old strategies that has become irrelevant, like my recent experience:

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mbr2gpt also has a validate option that might help avoid problems, though I tend to run a full filesystem check and backup beforehand just in case.

bba-tcg · Apr 30, 2025

mikeymikec said:
Me too, though I wonder if Windows setup can actually handle multiple drives in a decent manner now, it might be one of those sufficiently old strategies that has become irrelevant, like my recent experience:

Surprising improvements in Outlook (classic / Office)

The other day I was migrating a customer's setup from their old PC to a new one. Regarding Outlook, they were going from Outlook 2010 to Outlook 2024, involving a giant PST file and a POP3 mail setup (which is how they wanted to keep it). From experience, I've learned that the best way to...

forums.anandtech.com

---

mbr2gpt also has a validate option that might help avoid problems, though I tend to run a full filesystem check and backup beforehand just in case.

Windows probably can handle it better these days. If i had multiple NVMe drives in a PC, I'd likely test it to see.

I always do a chkdsk and validate beforehand converting a disk, though I've had a disk pass validation and still fail to convert.

Question WIndows 11 hardware support question, changing an existing SSD with partitions from MBR partition style to GPT partition style

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