A Full Guide to MBR2GPT.EXE Tool

Check out how to use and run the MBR2GPT.exe tool, its limitations, and troubleshooting tips in Windows 10 and 11.

If you have started a Windows 11 upgrade in your corporate environment, you may have heard about MBR2GPT. MBR2GPT.exe is a tool that helps convert the disk partition style on Windows PC from the legacy Master Boot Record (MBR) to GUID Partition Table (GPT) without changing or deleting data on the hard drive.

This article will teach you about the MBR2GPT tool for Windows 10 and 11 and how you can use it yourself.

Part 1. What Is MBR2GPT Tool on Windows 10/11?

MBR2GPT.EXE converts a disc from the Master Boot Record (MBR) partition style to the GUID Partition Table (GPT) partition style. It is designed to be run from a WinPE (Windows Preinstallation Environment) Command Prompt. However, with the /allowFullOS option, the program can also be launched from the entire Windows 10 operating system (OS).

The MBR2GPT tool can be found in the directory Windows\System32 on PCs running Windows 10 version 1703 or later and Windows 11.

Both Windows PE and the complete OS environment have this utility available. You must first upgrade the Windows PE image (winpe.wim, boot.wim) with the Windows ADK 1703, or a later version, in order to utilize this tool in a deployment task sequence using Configuration Manager or Microsoft Deployment Toolkit (MDT).

mbr2gpt tool

Part 2. How To Use the MBR2GPT Tool?

1. Converting Within Full Windows OS Environment

Open the command prompt by typing cmd in the search box of the Windows 10 toolbar. In the cmd elevated command prompt, type mbr2gpt /convert /disk: n /allowfullOS. The disk partition you wish to convert appears. Press Enter, and you are done.

mbr to gpt conversion in windows10

2. Converting Within Windows PE

The process is the same. However, here you have to type in different commands.

  • Type command mbr2gpt /convert /disk: n.
conversion in windows pe

Part 3. The Limitations of MBR2GPT

Though MBR2GPT looks like a day-savior tool, it does come with some limitations.

  • MBR2GPT is not at all the same as BIOS to UEFI conversion It converts partition layout, while the latter changes the system's firmware from Legacy BIOS to UEFI.
  • The MBR2GPT tool should only be run before the conversion of BIOS to UEFI during the upgrade, and most preferably in the Windows PE system. There can be an unsuccessful conversion encountered if the tool is run after the firmware is converted.
  • GPT or Legacy layouts are not officially supported. Hence, once you make the conversion using this tool, you may lack official support if something goes wrong.
  • You cannot undo the steps once the disk has been converted. Also, in case you have performed the layout during an upgrade, you cannot revert to a previous version of windows. This limitation is standard, irrespective of the brand of computer you are using.
  • If you wish to use the tool to its total capacity, you need to use the disk that needs to be converted with less than 4 partitions. In various tests, it was found that Dell models can create extra recovery partitions during an upgrade, which failed the conversion with MBR2GPT once the limit of partitions is reached before the upgrade.
  • You need to ensure you are providing the correct driver package for the model if you are utilizing the tool with a single sequence that might handle all hardware models. Additionally, you must confirm that the engine can take the variables you are providing. The setup will disregard incorrect driver package variables. As a result, another drawback we discovered is the drivers' accuracy.

Part 4. Troubleshooting When Using MBR2GPT

The tool can return various common errors. But don't worry, as you can resolve them in most cases. Here is the list of return codes you may get when using the MBR2GPT utility:

Return code
0 The conversion was completed successfully.
1 The conversion was canceled by the user.
2 The conversion failed due to an internal error.
3 The conversion failed due to an initialization error.
4 The conversion failed due to invalid command-line parameters.
5 The conversion failed due to an error in reading the geometry and layout of the selected disk.
6 The conversion failed because one or more volumes on the disk are encrypted.
7 The conversion failed because the geometry and layout of the selected disk didn't meet the requirements.
8 The conversion failed due to an error while creating the EFI system partition.
9 The conversion failed due to an error installing boot files.
10 The conversion failed due to an error while applying the GPT layout.
100 The conversion to the GPT layout succeeded, but some boot configuration data entries couldn't be restored.

Fix #1: MBR2GPT Disk Layout Validation Failed

mbr2gpt validation failed

This is one of the most common errors we find during the MBR to GPT conversion. It may be due to the wrong syntax or system you are using. MBR2GPT.exe only applies to Windows 10 version 1703 or later. The error can also occur if your system does not support the BIOS you are converting.

To solve this, check the following:

  • That your syntax is correct
  • Your system supports UEFI BIOS
  • Check the type of BIOS you are currently using
  • Check if your system is not Windows 7,8, 8.1, or earlier versions of Windows 10. It should be Windows 10 version 1703 or later, or Windows 11 if you want to use MBR2GPT

You can also refer to this video for a complete guide to fix the "MBR2GPT disk layout validation failed" error.

Fix #2: MBR2GPT Cannot Find OS Partition

There could be many technical reasons behind this error. The most common one is that your system has bad entries in the boot configuration. Check the video below to solve this problem quickly.

Here is also a step-by-step guide for you to fix “MBR2GPT can’t find OS partition”:

Step 1. Open the diskpart and check for any bad entries. Use the syntax as follows:

▸select disk 0: the operating system disk
▸list partition
▸select partition 2: because here partition 2 is the partition where the Windows OS is installed
▸assign drive letter= w (for example)
▸select partition 1: because here partition 1 is the system-reserved partition
▸assign drive letter= b (for example)

fix for cannot find os partition

After this, you can easily take a step ahead of the system boot partition files to examine the Windows system partition further and determine whether the boot folder is present.

Step 2. Use the command "X: Sources>dir /a w: " Run the command "X: Sources>dir /a b: " to verify the system-reserved partition if the necessary boot folders are not present.

verify boot information

Step 3. After locating the boot folder in the system partition or system reserved partition, you must use the command "X: Sources>dir /a b: Boot" to launch the bcdedit program and direct it to the location of the boot configuration data store you just located.

Step 4. Identify any invalid entries at this point. Type "X: Sources>bcdedit /store B:bootbcd /enum all" to run the command. There are numerous cues for incorrect or subpar entries. For instance, "unknown" might be found in a few entries. They might be left over from an earlier Windows installation or brought on by malicious software.

look for unknown entries

Step 5. Copy the bad entry's identification. Next, navigate to the store once more with bcdedit and instruct it to remove the error-prone entry using the copied identifier. Finally, take The Bad Entry Out.

taking the bad entry out

Step 6. To see if everything is working correctly now, try running the command "X: Sources>bcdedit /store B:bootbcd /enum all" once more. If everything goes as planned, use the MBR2GPT utility once more. This time, you can finish it successfully.

Check out this video to learn more about the process in a visual format.

Fix #3: MBR2GPT Is Not Recognized

The leading cause of this version is your Windows version. You will get this error if you run any version other than windows 10 or 11.

To fix this error, you may simply upgrade your windows to version 10, and this error will not occur again. You can check your Windows version using the System Information dialogue box.

checking the system information

Fix #4: MBR2GPT Cannot Find Room for the EFI System Partition

This error comes up when you don't have enough free space on your computer's system or C allocated drive. In some cases, this error can also occur if there is no unallocated disk space on your system.

You can remove this error by shrinking the C drive to form a new unallocated space. Then, you can move the unallocated space to the front partition of the disk. You can also use any third-party tool to perform this step. Make sure to back up data before proceeding.

mbr2gpt cannot find room

Summing up

We hope this article was an eye-opener for you. Remember that facing errors during MBR2GPT tool conversion is a typical process. You will get a chance to learn the intricacies of the computer system while using this tool. Good luck.

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