Starting with Windows 10 Creators Update v1703, the operating system includes a new command line tool, mbr2gpt.exe, which converts an MBR disk (Master Boot Record) to a GPT disk (GUID Partition Table) 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 working Windows 10 operating system (OS).
You can use MBR2GPT to 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.
Currently, the tool supports conversion of disks with installed Windows 10 version 1507, 1511, 1607 and 1703. It does not officially support Windows 7 or Windows 8, even in offline mode. Microsoft recommends you to upgrade to Windows 10 if you want to try the tool in action.
Offline conversion of system disks with earlier versions of Windows installed, such as Windows 7, 8, or 8.1 are not officially supported.
This tool can be use to convert any attached MBR-formatted disk to GPT, including the system disk.
Here is a brief description of the available command line parameters.
/validate Instructs MBR2GPT.exe to perform only the disk validation steps and report whether the disk is eligible for conversion.
/convert Instructs MBR2GPT.exe to perform the disk validation and to proceed with the conversion if all validation tests pass.
/disk: 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: 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:=Specifies additional partition type mappings between MBR and GPT. The MBR partition number is specified in decimal notation, not hexidecimal. 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.
/allowFullOS By 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.
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.
In the following example, disk 0 is validated for conversion. Errors and warnings are logged to the default location, %windir%.
Code:
X:\>mbr2gpt /validate /disk:0 MBR2GPT: Attempting to validate disk 0 MBR2GPT: Retrieving layout of disk MBR2GPT: Validating layout, disk sector size is: 512 MBR2GPT: Validation completed successfully
In the following example the MBR2GPT tool is used to convert disk 0 to GPT disk.
Code:
X:\>mbr2gpt /convert /disk:0
MBR2GPT will now attempt to convert disk 0. If conversion is successful the disk can only be booted in GPT mode. These changes cannot be undone!
MBR2GPT: Attempting to convert disk 0 MBR2GPT: Retrieving layout of disk MBR2GPT: Validating layout, disk sector size is: 512 bytes MBR2GPT: Trying to shrink the system partition MBR2GPT: Trying to shrink the OS partition MBR2GPT: Creating the EFI system partition MBR2GPT: Installing the new boot files MBR2GPT: Performing the layout conversion MBR2GPT: Migrating default boot entry MBR2GPT: Adding recovery boot entry MBR2GPT: Fixing drive letter mapping MBR2GPT: Conversion completed successfully MBR2GPT: Before the new system can boot properly you need to switch the firmware to boot to UEFI mode!
In the following example Windows 10 converted from Legacy BIOS to UEFI within booted Windows 10.
Code:
mbr2gpt /convert /allowfullOS
To view a list of options available when using the tool, type mbr2gpt /?
