Re: The MBR2GPT Disk Conversion Tool In Windows 10

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Elliott Davis

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Jul 10, 2024, 6:20:10 AM7/10/24
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The MBR2GPT Disk Conversion Tool in Windows 10

If you want to switch from the legacy BIOS firmware to the modern UEFI firmware on your Windows 10 device, you may need to convert your disk from the Master Boot Record (MBR) to the GUID Partition Table (GPT) partition style. MBR and GPT are two different ways of storing the partition information on a disk. MBR is an older standard that has some limitations, such as supporting only up to four primary partitions and a maximum disk size of 2 TB. GPT is a newer standard that overcomes these limitations and offers some advantages, such as supporting up to 128 primary partitions and a larger disk size, as well as enabling some security features like Secure Boot and Device Guard.

However, converting a disk from MBR to GPT usually requires deleting all the data on the disk and reinstalling Windows 10 from scratch. This can be a time-consuming and risky process that may result in data loss or system instability. Fortunately, there is a tool that can help you convert a disk from MBR to GPT without modifying or deleting any data on the disk or making a clean installation of Windows 10. This tool is called MBR2GPT and it is available in Windows 10 version 1703 or later.

The MBR2GPT Disk Conversion Tool in Windows 10


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What is MBR2GPT?

MBR2GPT is a command-line tool that is located in the Windows\\System32 directory on a computer running Windows 10 version 1703 or later. The tool can run from a Windows Preinstallation Environment (Windows PE) command prompt, or from the full Windows 10 operating system by using the /allowFullOS option. The tool can convert any attached MBR-formatted system disk to the GPT partition format, as long as the disk meets some prerequisites. The tool can also convert an MBR disk with BitLocker-encrypted volumes as long as protection has been suspended. The tool can convert operating system disks that have earlier versions of Windows 10 installed, such as versions 1507, 1511, and 1607, but only by performing an offline conversion. The tool can also be used in a deployment task sequence with Configuration Manager or Microsoft Deployment Toolkit (MDT), if the task sequence uses Windows PE version 1703 or later.

How does MBR2GPT work?

MBR2GPT works by adding the GPT components to the MBR partition without modifying the existing partition and maintaining the data untouched. The conversion process involves four main steps:

    • Validating the disk layout and geometry. The tool checks if the disk is currently using MBR, if there is enough space not occupied by partitions to store the primary and secondary GPTs, if there are at most three primary partitions in the MBR partition table, if one of the partitions is set as active and is the system partition, if the disk does not have any extended/logical partition, if the BCD store on the system partition contains a default OS entry pointing to an OS partition, if the volume IDs can be retrieved for each volume that has a drive letter assigned, and if all partitions on the disk are of MBR types recognized by Windows or have a mapping specified using the /map option. If any of these checks fail, the conversion will not proceed.
    • Creating the GPT components. The tool creates a new protective MBR, a new GPT header, and a new GPT partition table based on the information from the existing MBR partition table. The tool also creates an EFI system partition (ESP) and a Microsoft Reserved Partition (MSR) on the disk. The ESP is used to store the boot files for UEFI, while the MSR is used to reserve space for future use by Windows. The tool copies the boot files from the system partition to the ESP and updates the BCD store on the ESP to point to the OS partition. The tool also generates a random disk GUID for the GPT header and unique partition GUIDs for each GPT partition.
    • Applying policies. The tool applies various policies to prepare for booting in UEFI mode. These policies include setting attributes for each GPT partition, such as read-only or hidden attributes, setting the GPT partition type for each GPT partition, such as the ESP or the MSR, and setting the required UEFI NVRAM variables, such as the BootOrder and the Boot#### variables. The tool also sets the SAN policy to OnlineAll to ensure that all disks are online after booting in UEFI mode.
    • Finalizing the conversion. The tool marks the conversion as complete by setting a flag in the OS partition, which indicates that the disk has been successfully converted and can boot in UEFI mode. The tool also logs the conversion status and details in a log file located in %windir%\\setupact.log.

    How to use MBR2GPT?

    To use MBR2GPT, you need to open an elevated command prompt and type the following syntax:

    MBR2GPT [/validate] /disk: [/logs:] [/map:] [/allowFullOS]

    The parameters are explained as follows:

      • /validate: This option checks whether the disk is eligible for conversion, but does not perform the conversion. This option can be used in both Windows PE and full Windows 10 OS.
      • /disk:<disknumber>: This option specifies the disk number of the disk to be converted. You can use the diskpart command to list the disk numbers on your device.
      • /logs:<path>: This option specifies where to store the log files of the conversion. The default location is %windir%\\setupact.log and %windir%\\setuperr.log.
      • /map:<mappingtable>: This option specifies a custom mapping of MBR partition types to GPT partition types. The mapping table is a comma-separated list of pairs of MBR partition types and GPT partition GUIDs. For example, /map:0x07=ebd0a0a2-b9e5-4433-87c0-68b6b72699c7,0x17=af9b60a0-1431-4f62-bc68-3311714a69ad.
      • /allowFullOS: This option allows the tool to run from the full Windows 10 OS instead of Windows PE. When using this option, you must reboot the device for the conversion to complete.

      Here is an example of using MBR2GPT to convert disk 0 from MBR to GPT in Windows 10 OS:

      MBR2GPT /convert /disk:0 /allowFullOS

      After running this command, you need to reboot your device and change the firmware settings to boot in UEFI mode. You can also enable Secure Boot if your device supports it.

      Conclusion

      MBR2GPT is a useful tool that can help you convert a disk from MBR to GPT without losing data or reinstalling Windows 10. This can allow you to switch from BIOS to UEFI firmware and enjoy some benefits such as faster boot time, larger disk size, and better security. However, before using this tool, you should make sure that your device supports UEFI and that your disk meets the prerequisites for conversion. You should also backup your data and create a recovery drive in case something goes wrong during or after the conversion.

      If you want to learn more about MBR2GPT, you can visit the following links:

        • [MBR2GPT - Windows Deployment Microsoft Learn]
        • [How to convert MBR to GPT drive to switch BIOS to UEFI on Windows 10 Windows Central]
        • [Convert MBR to GPT with MBR2GPT Tool in Windows 10 V1703 or Later]
        • [What Is MBR2GPT Tool and How To Use It [Guide 2023] - Recoverit]
        • [Convert Windows 10 from Legacy BIOS to UEFI without Data Loss]
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