Windows 10 Creators Update 1703 includes a new tool to convert MBR disks to GPT disks

So I am working on converting a Windows 10 1703 installation that is installed on a MBR disk, and have been looking for the best way to convert it to a GPT disk, so that secure boot, credential guard, and device guard can be enabled. As you may or may not already know, if Windows 10 is installed on an MBR (Master Boot Record) disk, you can not take advantage of all the latest advances in security. Thankfully, Microsoft has included a tool called MBR2GPT.exe in the Windows\system32 directory. Although this tool is really supposed to be used from a PreInstallation Environment like WinPE, it can be used from inside a Windows 10 1703 Build 15063 installation if you use the command line switch /AllowFullOS.

However, it is not as easy to convert as one may think, especially if your first hard disk already has multiple partitions. This is a problem that I am working on fixing. I learned that running the command
MBR2GPT /validate /disk:0 /allowfullos
errors out for me and when I find the setuperr.log in the Windows directory, it says that the disk has too many partitions to convert to GPT. The log said this:
2017-04-02 17:29:34, Error ValidateLayout: Too many MBR partitions found, no room to create EFI system partition.
2017-04-02 17:29:34, Error Disk layout validation failed for disk 0
ValidateLayout: Too many MBR partitions found, no room to create EFI system partition.
Error Disk layout validation failed for disk 0

Therefore, I am going to have to blow away some partitions before converting this disk. This disk is an SSD with four partitions, but I have tried this from WinPE environment with a Disk that has only 2 partitions and it works. The problem with my SSD drive is that it has an MSR partition in the front, then the Windows C volume, then a Recovery partition, and then an HP Tools partition that I installed from an HP update for the BIOS.

Update: I went back and forth with the reader that commented below, via email and wanted to document how he fixed his problem so it could help someone else in the future. His first comment was :

I am getting an error when trying to do the validation:
ValidateLayout: Wrong boot partition count, expected 1 but found 0.

He then emailed me back and said that his OS Drive was on the first Physical Disk, but his boot partition aka system partition was on the second disk.

My next message to him was:

“Do you have any room to make another partition on the first drive?
I would try to shrink the OS Drive by like 500 mb, then create a new partition on the first drive, using FAT32 of 500mb, there is a way to label it MSR with diskpart, then try to copy the system files directly to that drive, but leave the system from the second disk in tact, so it will still boot, not sure if you can copy the boot files, but you can always try an in-place upgrade so you don’t lose any files. You want the MBR2GPT tool to think that the boot drive is on the first partition. You want the first drive to have two or three partitions, the FAT32 one where you copy the system and boot files over, the OS, and the Recovery drive if you need it. I don’t think I ever had the boot drive on another physical disk, but I have had to recreate the boot drive on my OS disk, and I used the macrium reflect rescue CD to rebuild the boot (System Drive for me). It makes it very easy, so I think it is possible. Let me know if you have any more questions.
Good luck
James

So he then tried this and came back and said :
That did the trick!
I created a new 500 mb partition using NTFS, copied the files from the old system partition. Ran mbr2gpt and everything works 🙂

Thank you so much !

Now I am not sure if secure boot will work now, because secure boot can be a little tricky to get going, but he was able to convert the first drive to GPT by shrinking the OS making a new partition on the OS Drive and copying the boot system partition from drive 2 to drive one. If anyone else has this problem in the future, try this… As far as getting secure boot enabled, that may just work, or it may require some more configuration. Hit me up if you need help with this.

2 thoughts on “Windows 10 Creators Update 1703 includes a new tool to convert MBR disks to GPT disks

  1. I am getting an error when trying to do the validation:
    ValidateLayout: Wrong boot partition count, expected 1 but found 0.

    Any idea what to do?

    • If you are still facing this error, I know that you need to have a small MSR partition in the front of the Windows partition. I was able to convert mine by simply deleting the 4th partition on my drive. But it sounds like you don’t have any boot partition, GPT requires a partition that is of the format FAT32. This is important. You must create a small partition with Diskpart that used the Fat32 filesystem. ( if not sure how big just use about 500mb. ) let me know if you are still having this problem.

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