MBR | GPT | Windows | Cmstechovation Enterprise | United States

Do you have a question on how to convert your main windows MBR harddrive to GPT in Windows 10?

Microsoft MBR to GPT


MBR2GPT.EXE converts a disk from the Master Boot Record (MBR) to the GUID Partition Table (GPT) partition style without modifying or deleting data on the disk. The tool is designed to be run from a Windows Preinstallation Environment (Windows PE) command prompt, but can also be run from the full Windows 10 operating system (OS) by using the /allowFullOS option.

MBR2GPT.EXE is located in the Windows\System32 directory on a computer running Windows 10 version 1703 (also known as the Creator's Update) or later.

The tool is available in both the full OS environment and Windows PE. To use this tool in a deployment task sequence with Configuration Manager or Microsoft Deployment Toolkit (MDT), you must first update the Windows PE image (winpe.wim, boot.wim) with the Windows ADK 1703, or a later version.


 You can use MBR2GPT to:

  • Convert any attached MBR-formatted system disk to the GPT partition format. You cannot use the tool to convert non-system disks from MBR to GPT.
  • Convert an MBR disk with BitLocker-encrypted volumes as long as protection has been suspended. To resume BitLocker after conversion, you will need to delete the existing protectors and recreate them.
  • Convert operating system disks that have earlier versions of Windows 10 installed, such as versions 1507, 1511, and 1607. However, you must run the tool while booted into Windows 10 version 1703 or later, and perform an offline conversion.
  • Convert an operating system disk from MBR to GPT using Configuration Manager or MDT provided that your task sequence uses Windows PE version 1703 or later.

Offline conversion of system disks with earlier versions of Windows installed, such as Windows 7, 8, or 8.1 are not officially supported. The recommended method to convert these disks is to upgrade the operating system to Windows 10 first, then perform the MBR to GPT conversion.

***Note:  After the disk has been converted to GPT partition style, the firmware must be reconfigured to boot in UEFI mode.  Make sure that your device supports UEFI before attempting to convert the disk***


​Disk Prerequisites

Before any change to the disk is made, MBR2GPT validates the layout and geometry of the selected disk to ensure that:

  • The disk is currently using MBR
  • There is enough space not occupied by partitions to store the primary and secondary GPTs:
    • 16KB + 2 sectors at the front of the disk
    • 16KB + 1 sector at the end of the disk
  • There are at most 3 primary partitions in the MBR partition table
  • One of the partitions is set as active and is the system partition
  • The disk does not have any extended/logical partition
  • The BCD store on the system partition contains a default OS entry pointing to an OS partition
  • The volume IDs can be retrieved for each volume which has a drive letter assigned
  • All partitions on the disk are of MBR types recognized by Windows or has a mapping specified using the /map command-line option

If any of these checks fails, the conversion will not proceed and an error will be returned.


Syntax

MBR2GPT /validate|convert [/disk:<diskNumber>] [/logs:<logDirectory>] [/map:<source>=<destination>] [/allowFullOS]

Options

OptionDescription
/validateInstructs MBR2GPT.exe to perform only the disk validation steps and report whether the disk is eligible for conversion.
/convertInstructs MBR2GPT.exe to perform the disk validation and to proceed with the conversion if all validation tests pass.
/disk:<diskNumber>Specifies the disk number of the disk to be converted to GPT. If not specified, the system disk is used. The mechanism used is the same as that used by the diskpart.exe tool SELECT DISK SYSTEM command.
/logs:<logDirectory>Specifies the directory where MBR2GPT.exe logs should be written. If not specified, %windir% is used. If specified, the directory must already exist, it will not be automatically created or overwritten.
/map:<source>=<destination>Specifies additional partition type mappings between MBR and GPT. The MBR partition number is specified in decimal notation, not hexadecimal. The GPT GUID can contain brackets, for example: /map:42={af9b60a0-1431-4f62-bc68-3311714a69ad}. Multiple /map options can be specified if multiple mappings are required.
/allowFullOSBy default, MBR2GPT.exe is blocked unless it is run from Windows PE. This option overrides this block and enables disk conversion while running in the full Windows environment.
Note: Since the existing MBR system partition is in use while running the full Windows environment, it cannot be reused. In this case, a new ESP is created by shrinking the OS partition.


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