Windows 10: 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!

:)

 

Partition Prerequisites for converting to GPT using MBR2GPT

Delete step 3. Step 4 will convert the system drive to GPT and convert the System Reserved partition (which legacy BIOS boots from) to an EFI System Partition (which UEFI boots from). After MBR2GPT completes that conversion, your computer will no longer boot in legacy BIOS mode. You will need to set the UEFI firmware to boot in UEFI mode before the computer will boot into the OS again.

After the system drive is converted to GPT and is booting in UEFI mode, then you can convert the other physical drives to GPT if you want to using third party partitioning programs like MiniTool Partition Wizard or AEOMI Partition Assistant.

After you backup your drive, presumably with a program like Macrium Reflect, make sure to also create the rescue drive (USB flash drive) with the same program so that you can boot the computer from that to restore the backup image if you need to. The rescue drive should be bootable in both legacy BIOS and UEFI modes.

I'll work on the steps to do the conversion manually and setting up your own EFI System Partition from scratch. I'm going to make a backup of my computer and do it myself to make sure I get the steps correct.

 

Cannot convert GPT to MBR.

Hi Michael,



I suggest you to follow the below steps and check if it helps.

This method you have to backup all your data and delete all partitions and volumes. Then use the
DISKPART command.

• Open command prompt and type in DISKPART and press Enter
• Then type in list disk (Note down the number of disk you want to convert to GPT)
• Then type in select disk number of disk
• Finally type in convert gpt.

Hope the information helps. Do reply if you need further assistance.

 

Convert only one partition on the disk from MBR to GPT

Follow the steps listed here on using GPTgen. He also lists how to create and restore backups.

Converting MBR to GPT without deleting your partitions