Can not convert MBR to GPT


  1. Regenrausch
    Posts : 2
    Windows 10
       New #1

    Can not convert MBR to GPT


    Hello,

    my Windows 10 system is running fine, however I always have to select the boot device because my UEFI does not recognize my SSD with the OS on it. Instead, the only default boot option is my 500x SSD, which is completely empty.

    I read some articles explaining that UEFI needs GPT to recognize the hard drive, but my 500x (which is recognized) is also MBR.

    I have tried the command mbr2gpt /convert, but after telling me "trying to convert..." It failed. And on diskmg the option for "convert to GPT" is not clickable.
    Can not convert MBR to GPT-capture.png
    Disk 0: CT500MX500SSD1
    Disk 1: Intenso SSD Sata III
    Disk 2: SanDisk SSD PLUS 240GB

    Windows 10 21H2 (OS Build 19044.1706)
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  3. cereberus
    Posts : 15,491
    Windows10
       New #2

    A limitation of mbr2gpt is that you can only have three primary partitions on a drive, as it has to create a new efi partition and there is a limit of 4 primary partitions on an mbr drive.

    Delete the 4GB primary partition (as it is empty), and mbr2gpt should then work.
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  4. Regenrausch
    Posts : 2
    Windows 10
    Thread Starter
       New #3

    Thank you very much cereberus, I It helped. My system is now booting normally without needing to select boot device. I UEFI I can also select the windows partition.

    However when It converted It also told me this message:

    "MBR2GPT: Failed to update ReAgent.xml, please try to manually disable and enable WinRE."
    "MBR2GPT: Before the new system can boot properly you need to switch the firmware to boot to UEFI mode!"

    I do not have any problems right now, but should I be aware of those messages?
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  6. Ghot
    Posts : 23,281
    Win 10 Home ♦♦♦19045.4355 (x64) [22H2]
       New #4

    All the 2nd message is saying, is that AFTER you convert to GPT... you will need to change the BIOS setting from Legacy to UEFI or the install won't boot.

    The BIOS setting has to match the drive type that Windows is installed on.
    GPT needs UEFI BIOS setting
    MBR needs Legacy BIOS setting.


    The setting will be somewhere on the Boot tab in your BIOS.


    This is from your motherboard manual (ASRock A320m), showing all the Boot tab settings.
    I don't really see a clear cut place to change the setting, but maybe someone else will.

    Can not convert MBR to GPT-image3.png







    Maybe this will help. This is from MY motherboard manual. It's a bit easier to understand.

    Can not convert MBR to GPT-image1.png




    On yours I don't see a "Boot Device Control" setting.

    On my motherboard... either of those options (in the RED boxes), under "Boot Device Control"
    will allow me to boot from a GPT disk.
    The "Legacy OPROM Only" option will only allow me to boot from an MBR disk.
    Last edited by Ghot; 20 May 2022 at 09:00.
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  7. boombastik
    Posts : 428
    Windows 11 pro X64 latest
       New #5

    The first message it simply says to you to recreate the windows recovery partion.
    Open an elevated command prompt.
    Copy and paste reagentc /disable into the elevated command prompt, and press Enter
    wait 10 seconds and then recreate it with:
    Copy and paste reagentc /enable into the elevated command prompt, and press Enter


    The second message it simply tells you to change the legacy mode to uefi but your motherboard do it automatically.
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  8. Megahertz
    Posts : 6,343
    Windows 11 Pro - Windows 7 HP - Lubuntu
       New #6

    boombastik said:
    The first message it simply says to you to recreate the windows recovery partion.
    Open an elevated command prompt.
    Copy and paste reagentc /disable into the elevated command prompt, and press Enter
    wait 10 seconds and then recreate it with:
    Copy and paste reagentc /enable into the elevated command prompt, and press Enter


    The second message it simply tells you to change the legacy mode to uefi but your motherboard do it automatically.

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