Convert Windows 10 from Legacy BIOS to UEFI without Data Loss  

Brink said:

I don't see anything wrong in Disk Management.

If you don't mind doing a clean install, you could certainly clean install with UEFI instead.

Clean Install Windows 10

Am trying to avoid that. Any thoughts on the Windows PE / using the CLI to convert the drive route? Does the recovery environment apparently being missing have anything to do with it? Several threads say it's not really an issue having it missing, but they also don't try converting the drive.

There are so many issues with that. I went to 10 from 7 and although I retrieved the '10' key (which is different than the 7 key was) I suspect the first hurdle to be a registration issue. There are some programs I have installed in which associated keys and profiles will be either a challenge or impossible to recreate (no, nothing illegal here.)

Krawk said:

Am trying to avoid that. Any thoughts on the Windows PE / using the CLI to convert the drive route? Does the recovery environment apparently being missing have anything to do with it? Several threads say it's not really an issue having it missing, but they also don't try converting the drive.

There are so many issues with that. I went to 10 from 7 and although I retrieved the '10' key (which is different than the 7 key was) I suspect the first hurdle to be a registration issue. There are some programs I have installed in which associated keys and profiles will be either a challenge or impossible to recreate (no, nothing illegal here.)

Repair Install Windows 10 with an In-place Upgrade I wonder if doing an in-place-repair upgrade where you keep your apps and files would resolve the issue. Make an image backup first Backup and Restore with Macrium Reflect

Then try the mbr2gpt after the repair install.

Krawk said:

Am trying to avoid that. Any thoughts on the Windows PE / using the CLI to convert the drive route? Does the recovery environment apparently being missing have anything to do with it? Several threads say it's not really an issue having it missing, but they also don't try converting the drive.

There are so many issues with that. I went to 10 from 7 and although I retrieved the '10' key (which is different than the 7 key was) I suspect the first hurdle to be a registration issue. There are some programs I have installed in which associated keys and profiles will be either a challenge or impossible to recreate (no, nothing illegal here.)

You've got plenty of room on your secondary drive. I would create a verified image backup of C: drive (you only need C: drive, no other partitions) using Macrium Reflect Free (you'll need a Macrium Reflect rescue USB drive). Then boot the computer from the Macrium Rescue Drive, wipe disk 0. Convert it GPT. Create an EFI System Partition (100 mb), restore the C: drive image to the rest of the drive. Run the fix windows boot problems utility from the Macrium Reflect restore menu.

Another source of problem might be no free (unallocated) space, mbr2gpt requires a small amount of free space at the front and end of drives.

Thanks @steve108 and @NavyLCDR -- Sounds like a repair is a safe first bet, then the Macrium option is a great second option.
I'm in the middle of a work rotation schedule so it will be a few days before I try these. Will report back.

steve108 said:

Repair Install Windows 10 with an In-place Upgrade I wonder if doing an in-place-repair upgrade where you keep your apps and files would resolve the issue. Make an image backup first Backup and Restore with Macrium Reflect

Then try the mbr2gpt after the repair install.

Here's the latest progress report. Does it look like I am safe to reboot now and enable UEFI in the bios, despite the error? A repair/upgrade in place was run and the third partition was created on disk 0.

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 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!

Krawk said:

Here's the latest progress report. Does it look like I am safe to reboot now and enable UEFI in the bios, despite the error? A repair/upgrade in place was run and the third partition was created on disk 0.

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 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!

Yes, it seems like the conversion was successful, so go for it

The solution to the ReAgent.xml is in here in post #2 : Reagentc failed , but first see if the PC boots as the error is not an issue for booting.

steve108 said:

Yes, it seems like the conversion was successful, so go for it

Thanks. Giving it a bit of time before I do so in case a second opinion chimes in but I do trust you! I know WinRE is the Recovery Environment.
In the thread about being unable to create a recovery drive, I've seen many people saying that the RE is less important in Windows 10.

This process has created a 4th 100Mb partition for the EFI.

Nothing wrong with waiting for a second opinion.

In the mean time, if you haven't see this: Enable or Disable Windows Recovery Environment in Windows 10