Windows 10: MBR to GPT conversion for boot disk - failing

Hello

Ive recently purchased a 16Gb optane memory module for my PC. Unfortunately to get it to run for me I need all my drives converting to GPT.

This was straight forward for my 500Gb data drive however it has proven to be more difficult for my boot drive.

As my current 120Gb boot drive was almost full, i took the opportunity to get a bigger 9250Gb) drive as i assumed I could set this a GPT from the off.

However, following guidance on this site: How to Clone MBR Disk to GPT Disk/SSD - EaseUS
I saw i needed to set my new 250gb drive up as MBR, and then clone my 120Gb boot to this disk before converting from MBR to GPT.

To do the conversion I followed command prompt> mbr2gpt /convert/ allowfullos process as outlined here:
How to convert MBR to GPT drive to switch BIOS to UEFI on Windows 10 | Windows Central

Unfortunately I get the following error after the conversion has failed:

MBR2GPT: Attempting to convert disk 0
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
MBR2GPT: Trying to shrink the OS partition
Cannot find room for the EFI system partition.
MBR2GPT: Conversion failed

C:\WINDOWS\system32>

Similarly Ive tried this with my original 120Gb boot disc seeing as ive got a clone and I get the same error message.

Can anyone help?

FYi im running W10 build 18363

:)

 

How to convert an MBR disk into a GPT disk

Hi,

Thanks for the reply.

This is an unexpected behavior, after you convert the disk from MBR to GPT, it shouldn’t convert back automatically, however you can try to convert the disk back to GPT format if you are on Windows 10 version 1703 or later using the inbuilt utility
MBR2GPT.EXE.

• Click on Start menu (Windows logo), type
  CMD.
  
• Right click on Command prompt and select
  Run as administrator.
  
• Type MBR2GPT /validate /AllowFullOS
  
• Once the validation is successful, execute the following command and check the results.
  
• Type MBR2GPT /Convert /AllowFullOS
  
• Once the conversion is successful, you must boot the computer into BIOS and change the BIOS mode to
  UEFI.
  

Disclaimer: Modifying BIOS/ complementary metal oxide semiconductor (CMOS) settings incorrectly can cause serious problems that may prevent your computer from booting properly.
Microsoft cannot guarantee that any problems resulting from the configuring of BIOS/CMOS settings can be solved. Modifications of the settings are at your own risk.

For more information about MBR2GPT utility, please refer to the article:
Convert MBR disk into GPT using MBR2GPT.EXE

Hope it helps.

Thanks,

Peer Samie

Microsoft Community-Moderator

 

clone MBR HD to bootable GPT partition?

Hi,

1. You cannot convert mbr to gpt without data loss. otherwise, you can follow directions here:

FROM WINDOWS RECOVERY CONSOLE:

To change a master boot record disk into a GUID partition table disk using a command line

• 
  Back up or move the data on the basic master boot record (MBR) disk you want to convert into a GUID partition table (GPT) disk.
  
• 
  Open an elevated command prompt (right-click Command Prompt, and then click Run as Administrator) and type diskpart. If the disk does not contain any partitions or volumes, skip to step 6.
  
• 
  At the DISKPART prompt, type list disk. Make note of the disk number you want to convert.
  
• 
  At the DISKPART prompt, type select disk <disknumber>.
  
• 
  At the DISKPART prompt, type clean.
  

2. I'd suggest converting your vista drive to a virtual machine, load that up on your windows 10 system and use a program like virtualbox to run it.

 

How to convert an MBR disk into a GPT disk

Hi,



Thanks you for writing to Microsoft Community Forums.



I understand how frustrating it could be when things do not work the way they are expected to.



GUID Partition Table (GPT) disks use Unified Extensible Firmware Interface (UEFI). TO make this conversion possible, your motherboard must support UEFI.

What is the exact model of system board?





I suggest to refer to the following documentation link and see if it helps.



Convert an MBR disk into a GPT disk



Note: Please back up your data before you convert the disk to GPT format.



While installing Windows from boot menu, you can access the command prompt and follow the instructions mentioned in the link.



Boot the computer from the installation media, on the initial setup screen, press the
Shift key and the f10 key together to access the command prompt. Execute the commands as given in the article. Once the commands are executed successfully, you can close the command prompt and start the installation by clicking
on Install now.



Hope it helps.



Thanks,

Peer Samie

Microsoft Community-Moderator