Best Way to Fix “MBR2GPT Cannot Find OS Partition” in Windows 10

MBR2GPT Cannot find OS Partition for Disk 0?

Hi, experts, when i trying to use MBR2GPT to convert my Win10 boot disk from MBR to GPT partition table,  CMD keeps failing with the "Cannot find OS Partition(s) for disk 0". I have read many articles but nobody offered a clear solution for this. Anyone can help me out? Thanks a lot!

For converting MBR to GPT on Windows, the MBR2GPT application may be the most practical option for the majority of users. In this case, the user just wishes to convert his disk from MBR to GPT, but, the Windows tool MBR2GPT shows "Cannot find OS partition(s) for disk 0". 

MBR2GPT.EXE is a tool to help users convert an operating system disk from the MBR to GPT partition style without modifying or deleting any data on the boot disk. You can run it from a Windows Preinstallation Environment (Windows PE) command prompt, or the full Windows 10 operating system (OS) by using the /allowFullOS option. It is available and located in the Windows\System32 directory on a computer running Windows 10 version 1703 or later.

To convert a system disk with earlier versions of Windows such as Windows 7, 8, or 8.1, you have to upgrade the operating system to Windows 10 first, then perform the MBR to GPT conversion. In particular, Microsoft declared that Windows 11 requires supporting UEFI if users plan to upgrade their Windows 10 to Windows 11 through the "Check for Update" feature. Thus, converting their MBR disk to GPT is also necessary.

Why MBR2GPT cannot find OS partition for disk 0?

In general, you can use the MBR2GPT command line tool to convert your system disk from MBR to GPT. After this is done, you can boot Windows in modern UEFI mode rather than the old BIOS Legacy mode, and you can make the fullest use of 2TB+ hard drive. However, sometimes, it does not work and prompts the error message saying "Cannot find OS partition for disk 0".

Missing BCD data on the OS partition or invalid entries in the Boot Configuration data frequently causes the "MBR2GPT failed to find OS partition" error. Furthermore, you may achieve the MBR2GPT conversion failed error if the system partition is inactive or if your computer fails to satisfy the prerequisites of MBR2GPT.

How to solve MBR2GPT cannot find OS partition via CMD

There could be many reasons behind this MBR2GPT conversion failure. To solve it, you can use DiskPart and some CMD orders.

Solution 1. Repair bad entries in the Boot Configuration Data

Step 1. Make use of diskpart and run the following commands to find out the OS partition and the system reserved partition and assign them a drive letter.

▸diskpart

▸select disk 0: the operating system disk

▸list partition

▸select partition 2: the partition where the Windows OS is installed

▸assign drive letter= w (or other available drive letter)

▸select partition 1: the system reserved partition

▸assign drive letter= b (or other available drive letter)

▸exit: exit the diskpart.exe

Step 2. Run the command “X: \Sources>dir /a w: \ “to take a further look into the Windows system partition to check whether there are the boot folder inside. If there is not required boot folders, then run the command “X: \Sources>dir /a b: \” to check the system reserved partition.

Step 3. After you find the boot folder in either system partition or system reserved partition, you need to run the “X: \Sources>dir /a b: \Boot” to invoke the bcdedit tool and point it to the boot configuration data store that you have found.

Step 4. Look out the invalid entries now. Run the command: “X: \Sources>bcdedit /store B:\boot\bcd /enum all”. There are many hints for bad or invalid entries. For example, you might find “unknown” in some entry. They can be the remnant of a previous Windows installation or caused by some vicious software.

Step 5. Copy the identifier of the bad entry. Then, point bcdedit to the store again and ask it to delete the bad entry using the copied identifier.

Step 6. Then you can try to run the “X: \Sources>bcdedit /store  B:\boot\bcd /enum all” command again to check whether all are OK now.

When everything goes well, try the MBR2GPT tool again. You can make it done successfully this time.

Solution 2. Repair BCD

According to some answers.microsoft.com forum members, corrupted BCD files may contribute to the MBR2GPT conversion failed error. In this circumstance, BCD can be repaired by following the steps below.

Step 1. Type cmd in the search bar, right-click the Command Prompt app, and select Run as administrator.

Step 2. In the elevated Command Prompt window, type the following command and hit Enter.

bcdboot C:Windows /s C:

If this command doesn’t work, you can try running the command “bcdboot c:Windows /f bios /s c:”.

Solution 3. Activate WinRE

Re-enabling WinRE may resolve the "MBR2GPT cannot locate OS partition for disk 0" error, according to some users. Attempt to make an effort.

Step 1. Reopen the elevated Command Prompt window in the manner described previously.

Step 2. Input the subsequent commands in the specified order, pressing Enter after each one:

• reagentc /disable
• reagentc /enable

Convert MBR to GPT with MBR2GPT best alternative

Refer to the above solution and you can solve the “cannot find os partitions for disk 0” in MBR2GPT.exe tool. However, it is too complicated and difficult to follow for most users. So, here we would like to share an easier tool to help you finish the MBR and GPT conversion. That is AOMEI Partition Assistant Professional. Compared with MBR2GPT, it owns the following advantages:

Finish the MBR to GPT conversion on an intuitive interface, easy to follow for both experts and newbies;

 Be able to work well on all editions of Windows 11/10/8/7;

 Support converting both system disk and non-system disk from MBR to GPT partition styles without deleting any data on the disk.

 Besides converting disk from MBR to GPT, it can also convert any disk from GPT to MBR, likewise, without modifying disk data.

Now, you can download its demo version for a free trial or simulation.

Notes:✎...

After the boot disk has been converted to GPT partition style, the firmware must be reconfigured from Legacy BIOS to UEFI.

 Make sure that your device supports UEFI before attempting to convert the system disk.

Step 1. Install and run AOMEI Partition Assistant Professional. Right-click the system disk and choose “Convert to GPT” or click the disk and choose "Convert to GPT" from the right column. 

Step 2. In the next window, click “OK” to confirm your operation.

Step 3. Back to the main interface, click on “Apply” to commit the pending operation.

If you want to convert MBR or GPT without loading operating system, you can first use this software to create a bootabale media, then boot computer from it and finish the conversion.

Summary

This page tells how to solve “MBR2GPT cannot find OS partition” on Windows 10. Besides, we also introduce another tool to help you easily get around such issues. The AOMEI Partition Assistant Professional also comes with many other functions: clone MBR disk to GPT disk, or GPT disk to MBR disk, clone partition, transfer OS between MBR and GPT disk, convert dynamic disk to basic disk without deleting volumes, and more. If you are running Windows Server, please switch to the Server edition.

FAQs about MBR2GPT

Is it safe to use the MBR2GPT tool to convert my disk? While the MBR2GPT tool is designed to be safe, there is still a risk of data loss or corruption during the conversion process. It's essential to back up your important files and data before converting your disk.

How long does the MBR2GPT conversion process typically take? The conversion process can take anywhere from a few minutes to several hours, depending on the size of your disk and the speed of your system.

Can I cancel the MBR2GPT conversion process once it's started? No, once the MBR2GPT conversion process has started, it's recommended to let it complete. Canceling the process can result in a corrupted disk or data loss.