MBR2GPT fails to convert to GPT despite resizing partitions.

I'm trying to use MBR2GPT to enable UEFI secure boot on my system drive (which is currently booting in Legacy mode, Windows 10 Pro 21H1). The process fails repeatedly, returning the following error:

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

I've tried using EaseUS Partition Master to expand the System Reserved partition to 1 Gb, and shrunk my C drive by 2 Gb which I have left unallocated, but the error persists. I've also trimmed and defragmented my SSD, which makes no difference. Here's a copy of the log file generated by MBR2GPT:

2021-06-28 06:20:11, Info MBR2GPT was explicitly asked to run in full OS mode.
2021-06-28 06:20:11, Info MBR2GPT: System disk number is 5
2021-06-28 06:20:11, Info MBR2GPT: Attempting to convert disk 5
2021-06-28 06:20:11, Info MBR2GPT: Retrieving layout of disk
2021-06-28 06:20:11, Info MBR2GPT: Initial partition information
2021-06-28 06:20:11, Info ===========================================================
2021-06-28 06:20:11, Info Partition layout for disk: 5
2021-06-28 06:20:11, Info Partition style : MBR
2021-06-28 06:20:11, Info MBR signature: 3933125689
2021-06-28 06:20:11, Info Number of partitions : 3
2021-06-28 06:20:11, Info ===================PARTITION===============================
2021-06-28 06:20:11, Info Number: 1
2021-06-28 06:20:11, Info Type: 7
2021-06-28 06:20:11, Info Boot: Yes
2021-06-28 06:20:11, Info Recognized: Yes
2021-06-28 06:20:11, Info Style: 0
2021-06-28 06:20:11, Info Offset: 1048576
2021-06-28 06:20:11, Info Length: 1084227584
2021-06-28 06:20:11, Info Volume: \\?\Volume{ea6ebc39-0000-0000-0000-100000000000}\
2021-06-28 06:20:11, Info Drive: None
2021-06-28 06:20:11, Info NT Path: \Device\HardDisk5\Partition1
2021-06-28 06:20:11, Info ===================PARTITION===============================
2021-06-28 06:20:11, Info Number: 2
2021-06-28 06:20:11, Info Type: 7
2021-06-28 06:20:11, Info Boot: No
2021-06-28 06:20:11, Info Recognized: Yes
2021-06-28 06:20:11, Info Style: 0
2021-06-28 06:20:11, Info Offset: 1085276160
2021-06-28 06:20:11, Info Length: 996431364096
2021-06-28 06:20:11, Info Volume: \\?\Volume{ea6ebc39-0000-0000-0000-b04000000000}\
2021-06-28 06:20:11, Info Drive: C:\
2021-06-28 06:20:11, Info NT Path: \Device\HardDisk5\Partition2
2021-06-28 06:20:11, Info ===================PARTITION===============================
2021-06-28 06:20:11, Info Number: 3
2021-06-28 06:20:11, Info Type: 39
2021-06-28 06:20:11, Info Boot: No
2021-06-28 06:20:11, Info Recognized: Yes
2021-06-28 06:20:11, Info Style: 0
2021-06-28 06:20:11, Info Offset: 999664123904
2021-06-28 06:20:11, Info Length: 537919488
2021-06-28 06:20:11, Info Volume: \\?\Volume{ea6ebc39-0000-0000-0000-a0c0e8000000}\
2021-06-28 06:20:11, Info Drive: None
2021-06-28 06:20:11, Info NT Path: \Device\HardDisk5\Partition3
2021-06-28 06:20:11, Info ===========================================================
2021-06-28 06:20:11, Info ESP partition size will be 104857600
2021-06-28 06:20:11, Info MBR2GPT: Validating layout, disk sector size is: 512 bytes
2021-06-28 06:20:11, Info BCD: Opening store. Flags: 0x0
2021-06-28 06:20:11, Info BCD: Store path: "\??\GLOBALROOT\device\harddisk5\partition1\Boot\BCD"
2021-06-28 06:20:11, Info BCD: Loaded hive at BCD00000000
2021-06-28 06:20:11, Info BCD: Opening object {9dea862c-5cdd-4e70-acc1-f32b344d4795}
2021-06-28 06:20:11, Info FindOSPartitions: Default boot entry: {C33C746F-C837-11EA-BD7B-5CF370878565}
2021-06-28 06:20:11, Info BCD: Opening object {c33c746f-c837-11ea-bd7b-5cf370878565}
2021-06-28 06:20:11, Info VERBOSE: Device path: \Device\HarddiskVolume9
2021-06-28 06:20:11, Info VERBOSE: Dos path: \\?\GLOBALROOT\Device\HarddiskVolume9
2021-06-28 06:20:11, Info FindOSPartitions: Volume name for the default boot entry: \\?\Volume{ea6ebc39-0000-0000-0000-a0c0e8000000}\
2021-06-28 06:20:11, Info BCD: BcdGetElementDataWithFlags: Failed to open key.Object: {c33c746f-c837-11ea-bd7b-5cf370878565} Type: 14000008 Status: c0000034
2021-06-28 06:20:11, Info FindOSPartitions: No Recovery sequence found.
2021-06-28 06:20:11, Info FindOSPartitions: Default boot entry locale: en-GB
2021-06-28 06:20:11, Info Bitlocker protection for C:\ is either off or suspended.
2021-06-28 06:20:11, Info Unique ID recap for volumes:
2021-06-28 06:20:11, Info Volume name: \\?\Volume{ea6ebc39-0000-0000-0000-100000000000}
2021-06-28 06:20:11, Info Unique ID size: 12
2021-06-28 06:20:11, Info Volume name: \\?\Volume{ea6ebc39-0000-0000-0000-b04000000000}
2021-06-28 06:20:11, Info Unique ID size: 12
2021-06-28 06:20:11, Info Volume name: \\?\Volume{ea6ebc39-0000-0000-0000-a0c0e8000000}
2021-06-28 06:20:11, Info Unique ID size: 12
2021-06-28 06:20:11, Info MBR2GPT: System partition cannot be removed in full OS mode, leaving it untouched.
2021-06-28 06:20:11, Info MBR2GPT: Trying to shrink the OS partition
2021-06-28 06:20:12, Warning MBR2GPT: Partition final size is: 537919488 (initial size was 537919488), cannot rely on this space
2021-06-28 06:20:12, Error Cannot find room for the EFI system partition.
2021-06-28 06:20:12, Info MBR2GPT: Partition information at error point
2021-06-28 06:20:12, Info ===========================================================
2021-06-28 06:20:12, Info Partition layout for disk: 5
2021-06-28 06:20:12, Info Partition style : MBR
2021-06-28 06:20:12, Info MBR signature: 3933125689
2021-06-28 06:20:12, Info Number of partitions : 3
2021-06-28 06:20:12, Info ===================PARTITION===============================
2021-06-28 06:20:12, Info Number: 1
2021-06-28 06:20:12, Info Type: 7
2021-06-28 06:20:12, Info Boot: Yes
2021-06-28 06:20:12, Info Recognized: Yes
2021-06-28 06:20:12, Info Style: 0
2021-06-28 06:20:12, Info Offset: 1048576
2021-06-28 06:20:12, Info Length: 1084227584
2021-06-28 06:20:12, Info Volume: \\?\Volume{ea6ebc39-0000-0000-0000-100000000000}\
2021-06-28 06:20:12, Info Drive: None
2021-06-28 06:20:12, Info NT Path: \Device\HardDisk5\Partition1
2021-06-28 06:20:12, Info ===================PARTITION===============================
2021-06-28 06:20:12, Info Number: 2
2021-06-28 06:20:12, Info Type: 7
2021-06-28 06:20:12, Info Boot: No
2021-06-28 06:20:12, Info Recognized: Yes
2021-06-28 06:20:12, Info Style: 0
2021-06-28 06:20:12, Info Offset: 1085276160
2021-06-28 06:20:12, Info Length: 996431364096
2021-06-28 06:20:12, Info Volume: \\?\Volume{ea6ebc39-0000-0000-0000-b04000000000}\
2021-06-28 06:20:12, Info Drive: C:\
2021-06-28 06:20:12, Info NT Path: \Device\HardDisk5\Partition2
2021-06-28 06:20:12, Info ===================PARTITION===============================
2021-06-28 06:20:12, Info Number: 3
2021-06-28 06:20:12, Info Type: 39
2021-06-28 06:20:12, Info Boot: No
2021-06-28 06:20:12, Info Recognized: Yes
2021-06-28 06:20:12, Info Style: 0
2021-06-28 06:20:12, Info Offset: 999664123904
2021-06-28 06:20:12, Info Length: 537919488
2021-06-28 06:20:12, Info Volume: \\?\Volume{ea6ebc39-0000-0000-0000-a0c0e8000000}\
2021-06-28 06:20:12, Info Drive: None
2021-06-28 06:20:12, Info NT Path: \Device\HardDisk5\Partition3
2021-06-28 06:20:12, Info ===========================================================
2021-06-28 06:20:12, Info MBR2GPT: Conversion failed

This is a screenshot of the partition layout of my system drive:



Any suggestions would be welcome, otherwise it looks like I'll have to completely wipe my PC when the Windows 11 update drops!

System partition cannot be removed in full OS mode, leaving it untouched.

Try running mbr2gpt from boot media

Steve C said:

Try using MiniTool Partition Wizard - I use the portable version. You probably know you also need to enable secure boot in the BIOS.

Try running mbr2gpt from boot media

Tried all of that already, sadly.. Same error every time.

SIW2 said:

Try running mbr2gpt from boot media

Shutdown and detach all other drives (SATA or power cable)
As @SIW2 suggested, boot from a Win 10 installation drive, launch a CMD window (Shift+F10) and run:
MBR2GPT /validate

and

MBR2GPT /convert

run:

Code:

reagentc /disable

Restart the computer, delete the Recovery Partition, then run:

Code:

reagentc /enable
mbr2gpt /convert /allowfullos

Thanks for the suggestions, folks. I'm not worrying about it too much at the moment, since I'm not planning to upgrade to Windows 11 until at least 6 months after release to allow them to get the worst of the bugs out of it. I've tried most of what has been suggested except deleting the recovery partition; I REALLY don't want to mess with the boot sector or the recovery partition any more than I absolutely have to because I could end up bricking the entire system and have to wipe the whole damned thing. If I have to reformat to upgrade, then I'll cross that bridge when I come to it.

The boot settings on my Asus ROG Crosshair VII Hero are currently set to "UEFI and Legacy OPROMS". I tried switching it to "UEFI only", but that greyed-out all boot options in the BIOS and the system wouldn't boot. The only way I can get the thing to boot is in UEFI Legacy mode, which is screwing up the compatibility checker. I'm guessing that before launch, Microsoft will have to include an automated tool to detect and convert MBR boot sectors during installation, because 99% of regular users don't even know how to get into their BIOS settings, let alone start messing about with partitions and command prompts.

I'm not losing sleep over it until after the launch anyway.. Worst case scenario: I back up everything, delete every partion on every drive and reformat the whole damn lot. Then I'll switch the BIOS to "UEFI only" before attempting to install Win 11. I think AddRAM is right, though.. Those won't be the final requirements. They're going to HAVE to simplify or automate a lot of that stuff otherwise the launch will be a fiasco. I still remember the Great Windows Vista Catastrophe, and I'm guessing Microsoft does too..

How to install Windows (7, 8.x, or 10) in UEFI mode.

Reset BIOS or load defaults.
Set Disk mode to AHCI, not RAID
Set OS to UEFI or Legacy/UEFI
Disable fast boot and secure boot (you can enable after installation)


Windows can be installed in two ways: Legacy-MBR or UEFI-GPT
To install as Legacy-MBR you must boot the installation drive as Legacy
To install as UEFI-GPT you must boot the installation drive as UEFI.

On a new MB, you should install as UEFI-GPT
Detach any other drives (SATA or Power cable) from the MB.

During POST, press F? to launch the boot menu. You will see two options for the USB drive. USB UEFI (Name) and USB (Name). Select USB UEFI (Name).
Go to install and delete ALL partitions on the SSD till you have one and only one unallocated space and then proceed.
If you don't want to use MS account, don't enable updates or connect to the internet during installation.