MBR2GPT | Too many MBR partitions found, no room to create EFI system partition

When you convert your MBR disk to GPT using MBR2GPT, the error “Too many MBR partitions found” may occur. Here’s the relevant info from the log:

Error     ValidateLayout: Too many MBR partitions found, no room to create EFI system partition.
Error     Disk layout validation failed for disk 2

This error occurs because there are already four primary partitions on that disk. MBR supports a maximum of four primary partitions. So, MBR2GPT cannot create the EFI partition.

See also “Disk prerequisites” on this page:

• MBR2GPT | Microsoft Learn: https://learn.microsoft.com/en-us/windows/deployment/mbr-to-gpt

It states, “Ensure that: There are at most three primary partitions in the MBR partition table.”

Resolution

To resolve the issue, you need to delete one of the partitions. If that partition has important data, please back it up to a different partition beforehand. If you have multiple Recovery partitions, as in the screenshot above, the inactive Recovery partition can be deleted using the diskpart command-line.

To determine which Recovery partition is used, run reagentc /info in an admin Command Prompt in Windows. Note the disk # and partition #. The other partition can be deleted.

You should now be able to convert to GPT using the MBR2GPT command. Here’s a sample MBR2GPT output after deleting one of the Recovery partitions:

C:\WINDOWS\system32>mbr2gpt /convert /disk:2 /allowfullos

MBR2GPT will now attempt to convert disk 2.
If conversion is successful the disk can only be booted in GPT mode.
These changes cannot be undone!

MBR2GPT: Attempting to convert disk 2
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
Call WinReReapir to repair WinRE
MBR2GPT: Failed to update ReAgent.xml, please try to  manually disable and enable WinRE.
MBR2GPT: Before the new system can boot properly you need to switch the firmware to boot to UEFI mode!

I hope that the above information helps.