According to How can I migrate a Windows 10 from BIOS/MBR boot to UEFI/GPT without reinstalling? I can convert my system disk to GPT without reinstalling using the MBR2GPT tool, provided by Windows 10 CU. I'm also using Windows 10 Creators update at the moment.

I tried and I got an error about "not finding the OS partition".

This is the complete log:

2017-06-14 00:26:34, Info                         MBR2GPT was explicitly asked to run in full OS mode.
2017-06-14 00:26:34, Info                         MBR2GPT: System disk number is 0
2017-06-14 00:26:34, Info                         MBR2GPT: Attempting to validate disk 0
2017-06-14 00:26:34, Info                         MBR2GPT: Retrieving layout of disk
2017-06-14 00:26:34, Info                         MBR2GPT: Initial partition information
2017-06-14 00:26:34, Info                         ===========================================================
2017-06-14 00:26:34, Info                         Partition layout for disk: 0
2017-06-14 00:26:34, Info                         Partition style          : MBR
2017-06-14 00:26:34, Info                         MBR signature: 1967564465
2017-06-14 00:26:34, Info                         Number of partitions     : 2
     Number: 1
       Type: 7
       Boot: Yes
 Recognized: Yes
      Style: 0
     Offset: 1048576
     Length: 499621322752
     Volume: \\?\Volume{7546a6b1-0000-0000-0000-100000000000}\
      Drive: C:\
    NT Path: \Device\HardDisk0\Partition1
     Number: 2
       Type: 7
       Boot: No
 Recognized: Yes
      Style: 0
     Offset: 499628171264
     Length: 477078016
     Volume: \\?\Volume{7546a6b1-0000-0000-00e0-285474000000}\
      Drive: None
    NT Path: \Device\HardDisk0\Partition2
ESP partition size will be 104857600
MBR2GPT: Validating layout, disk sector size is: 512 bytes
Opening store. Flags: 0x0
Store path: "\??\GLOBALROOT\device\harddisk0\partition1\Boot\BCD"
Loaded hive at BCD00000000
Opening object {9dea862c-5cdd-4e70-acc1-f32b344d4795}
FindOSPartitions: Default boot entry: {ECE3CBB0-2B25-11E7-9886-AC950A4FD9A0}
Opening object {ece3cbb0-2b25-11e7-9886-ac950a4fd9a0}
VERBOSE: Device path: \Device\HarddiskVolume1
VERBOSE: Dos path: \\?\GLOBALROOT\Device\HarddiskVolume1
FindOSPartitions: Volume name for the default boot entry: \\?\Volume{7546a6b1-0000-0000-0000-100000000000}\
Opening object {1eb788fe-2b26-11e7-9886-ac950a4fd9a0}
GetOSDeviceVolume: Cannot get NT path for entry.[gle=0x000000ea]
FindOSPartitions: Cannot get volume name for the recovery boot entry. Error: 0x000000EA[gle=0x000000ea]
Cannot find OS partition(s) for disk 0[gle=0x000000ea]

It's not clear to me what's happening.

I know that my system originally had another SSD, from which I moved the OS to the current one using a Samsung tool and that later was used for Hackintosh with Chameleon (UEFI) bootloader. Now that disk is gone.

Still, Windows 10 is booting fine (without Secure Boot, of course). Why is the OS partition not found?

Important information

Since the question was asked, I formatted and started from scratch. I won't be able to test any answer, therefore no answer will be accepted. Anyone competent in the matter should use the opportunity to vote up or down any answer that will be eventually posted.

  • @Ramhound tried both. I used Windows PE from a usb stick, or Windows itself
    – FarO
    Jun 14, 2017 at 5:29
  • which windows 10 build do you use? do you also use GRUB to boot linux? Jun 14, 2017 at 15:46
  • @magicandre1981 I use Windows 10 Creators update, and I had in the second SSD OS X with a Chameleon UEFI bootloader. Now the second disk is gone. I edited.
    – FarO
    Jun 14, 2017 at 16:27

4 Answers 4


To clarify @merle 's VERY helpful answer - I had to run the command below to copy my working EFI boot data to a place where mbr2gpt could find it.

bcdboot c:\Windows /f bios /s c:

Once you've done this, you should be able to run mbr2gpt successfully.

Note: My system was already booting in UEFI mode to a MBR disk, which is why there was no BCD data in the typical location. This should fix that issue and allow mbr2gpt to do it's thing.

  • Welcome to Super User, and thanks for trying to help with this thread. For future reference, clarifying another post is best done in a comment (requires a little more rep), or by proposing an edit to the other answer to expand it with supplemental, clarifying information. Answer posts are really intended to be complete, standalone solutions.
    – fixer1234
    Dec 12, 2018 at 8:12
  • 1
    Thanks - I had tried to comment, but was a new user so couldn't. Thought it was a good compromise to still add the info to the page, rather than leave people without a complete answer. Will do that for sure once I have enough rep. Dec 13, 2018 at 23:34
  • 2
    This is a very important information and the "right way" to copy those files. The other answer looks like "just copy from here to there" but that is dangerouse at best.
    – T-Me
    Apr 25, 2019 at 12:30
  • 2
    I've tried everything, and almost gave up and reinstalled. This worked for me, and mbr2gpt converted the partition after this.
    – GlassFish
    Aug 1, 2021 at 17:17

I have tried all of the mentioned solutions, but none of them worked for me. However, I found out what was the main reason for the problem and solved it. When I ran diskpart and saw the details of partitions, I found that only system reserved partition is marked "Active" while The "C" partition wasn't, so I just set it to Active then ran mbr2gpt and it worked.

  1. Run CMD.
  2. Type "diskpart" without the quotes.
  3. Type "list disk".
  4. Type "select disk #" replace the # with the disk number you want.
  5. Type "list partition".
  6. Type "select partition #" replace the # with the number of the system partition, not system reserved.
  7. Type "detail partition".
  8. You will see partition details. If you see "No" in front of "Active", then type "Active".

And you are good to go!

  • This worked for me! I'm not sure if it's because I also tried the bcdboot command from @Vince above first and then this was needed also, or this was the whole problem. Thanks for the help everyone.
    – evilhomer
    Sep 21, 2021 at 9:57

For my situation I was booting UEFI/MBR and I suspect that this may be the case too since you were using Chameleon UEFI bootloader.

MBR2GPT.exe assumes BIOS boot and checks the BIOS BCD store at

[System Partition]\Boot\BCD

instead of finding out where the actual system store resides. My BIOS BCD had invalid entries so MBR2GPT rightfully complained that it couldn't find the non-existent recovery volume. I replaced the BIOS BCD with the EFI BCD from

[System Partition]\EFI\Microsoft\Boot

and was able to run MBR2GPT.

C:\Windows\system32>MBR2GPT.EXE /convert /allowfullos

MBR2GPT will now attempt to convert the default book disk.
If conversion is successful the disk can only be booted in GPT mode.
These changes cannot be undone!

MBR2GPT: Attempting to convert disk 3
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
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!

After trying the other suggestions and failing, I found this alternative solution to the problem of migrating Windows from BIOS/MBR boot to UEFI boot:

  1. Make a disaster recovery plan. Maybe clone the drive.
  2. Boot to Ubuntu Live, and backup the OS partition with ntfsclone.
  3. Install clean install of Windows with UEFI boot.
  4. Boot to Ubuntu Live, and restore the OS partition with ntfsclone.

This was my experience (YMMV):

  • ~100 min to backup ~550GB OS partition to USB connected HDD
  • ~25 min to install Windows from USB thumbdrive
  • ~120 min to restore

Here's example usage of ntfsclone:

ntfsclone --save-image --output /mnt/storage/windows.ntfsclone /dev/sda2
ntfsclone --restore-image --overwrite /dev/sda3 /mnt/storage/windows.ntfsclone
  • 1
    This has nothing to do with the question.
    – FarO
    Nov 23, 2022 at 13:06
  • @FarO - The primary use case for mbr2gpt is move the Windows OS from MBR/BIOS boot to UEFI boot, and you need to do this if you want to upgrade to Windows 11. I encountered the exact same symptoms as the OP, and for the same reason. Like many others, I installed Windows 7 on a small SSD, and disposed of the recovery partition. Later, I upgraded to Windows 10, and then even later, I wanted to upgrade to Windows 11. Without having already proven this solution - I would not assume that it would work. The boot processes of Windows (or any OS) are very esoteric and temperamental.
    – p.elsie
    Nov 23, 2022 at 15:25
  • With two drives, which I had - I could have skipped a step. Step1: Install clean install of Windows with UEFI boot to new drive. Step2: Clone OS partition from old drive on to new drive.
    – p.elsie
    Nov 23, 2022 at 19:22
  • The question is about that tool and your answer is to avoid using the tool. It is not an answer to the question.
    – FarO
    Nov 24, 2022 at 18:44
  • Sorry, change step 3 to: Install clean install of Windows with MBR boot. After completing step 4, the MBRGPT will work, since your system will now meet the requirements for using MBR2GPT. It will have a functional boot recover partition, and it will still have all your programs, files, and OS settings and customizations.
    – p.elsie
    Dec 18, 2022 at 16:05

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