Converting MBR to GPT error

Topic

New Reply

I have a Win 10 1803 system that was upgraded in place from Win 7 some time ago. The HD is an MBR disk so 1809 won’t install. I have tried to validate the disk with MBR2GPT but get the following output and error:

C:WINDOWSsystem32>mbr2gpt /validate /allowfullos

MBR2GPT: Attempting to validate disk 0

MBR2GPT: Retrieving layout of disk

MBR2GPT: Validating layout, disk sector size is: 512 bytes

Cannot find OS partition(s) for disk 0

Disk Manager is shown in the attachment below:

I’d like to use MBR2GPT to avoid having to perform a full clean install, but am not sure what to do to fix the above error.

 

Reply | Quote

Replies

The “cleanest” way to get it done requires a rescue disk that can launch a Command Prompt, and restore image files. Create a complete drive image of the hard drive you’re trying to convert, boot into your rescue disk, open Command Prompt and then DISKPART.  In DISKPART type (WOTQ) “list disk” and hit enter.  Find your target disk and use that number to type (WOTQ) “sel disk (your disk number)” and hit enter.

Your target disk now has focus.  First type (WOTQ) “clean” and hit enter; after that is successful, type (WOTQ) “convert gpt” and hit enter.  When that is successful, you need to create an EFI partition.

Still in DISKPART, type (WOTQ) “create partition efi size=400” and hit enter.  Next you’ll need to populate that EFI partition, and the easiest way to do that is to do a clean install of Windows; don’t worry, it’ll just be temporary.  When your clean install is complete and successfully boots into Windows, you can use your rescue disk to restore your complete hard drive image, leaving the EFI partition in place.  I don’t know what imaging software you’re using, but these days all imaging software is GPT aware, and knows how to deal with it.

You may have to work through some boot issues, but not necessarily.  The EFI partition points to the generic \Windows\System32\Winload.efi to boot Windows, which should just work.

Always create a fresh drive image before making system changes/Windows updates; you may need to start over!

We all have our own reasons for doing the things that we do with our systems; we don't need anyone's approval, and we don't all have to do the same things.

We were all once "Average Users".

Computer Specs

1 user thanked author for this post.

Dave

Reply | Quote

Thanks much for all the help. I’ll give this a shot in the next couple of days.

I use Macrium Reflect full for images and so have the rescue media it creates which I’m assuming will suffice. I also assume from your description that it doesn’t matter which Win 10 version I use for the clean load. I have a usb install of 1809 saved so I’m anticipating using that.

Thanks again.

Reply | Quote

I just ran into this problem last month!  (long time lurker, first time poster)

To fix it, I assigned letter S to the System Reserved partition, then in an administrative command prompt, ran: “bcdboot C:\Windows /s S: /f ALL” .  Yeah, even with Windows running.  Let me know if you need more info/detail.

In my case at least, this was because somehow I had an EFI setup even though it was an MBR disk.  Yeah, I didn’t know that was possible!  After that, mbr2gpt worked fine.

Of course, this may not be your exact problem and so it may not fix it, but I don’t think it will ruin anything.  It’s definitely easier than doing a complete reimage and install of Windows.  Standard disclaimers about backing stuff up and I’m not responsible for unexpected problems, of course.

1 user thanked author for this post.

Dave

Reply | Quote

Thanks, I may give that a try.

Reply | Quote

Finally got around to trying this out, it works great, thanks very much.

I did run into some non-boot conditions, but all it required was locating the correct boot partition and reordering the  boot sequence. Thanks again this saved a lot of work.

2 users thanked author for this post.

Qeyleb, Elly

Reply | Quote

Thanks for reporting your success!  I’m happy my problem was similar enough to be applicable.

Glad you were able to figure out the non-boot conditions with not too much trouble.

Reply | Quote

Vejam a solução em: (translated: see soultion at:)
https://www.youtube.com/watch?v=E2a5Uqj02OM

Mod Edit: Translation and change to URL

Reply | Quote