Quick story
There was one user who decided to use a 3TB hard drive. At that time, his computer
used Legacy boot. He knew that he had to convert
to GPT disk in order to use the full 3TB capacity. Then he used DiskPart.exe
to convert MBR to GPT, but he received an error message:
The operation is not allowed on a disk that contains a pagefile volume.

He even disabled page files in Control Panel and deleted the file c:\pagefile.sys in
File Explorer to no valid. What did he miss?
The truth is that DiskPart.exe can only convert an empty hard disk, not a partition,
to GPT or MBR partition style. Therefore, if you ever need to convert a hard drive
to MBR or GPT with DiskPart.exe, you need to use “clean” command to delete all
partitions on that disk before using “convert gpt”. However, certainly, you cannotwipe a hard drivecontaining Windows system which is now running.
Do it the right way
As mentioned, this method will get everything on the disk deleted. You’d better create a
backup of the hard drive before applying the following steps.
1. Boot your computer into BIOS to enable UEFI boot mode
and exit.
2. Boot your computer from a Windows installation CD or USB
disk.
3. At the screen to select where to install Windows, press
Shift + F10 to open a command prompt window.

4. Type the following:
Diskpart
List disk
Select disk [disknumber]
Clean
Convert gpt

5. Then this convert MBR to GPT issue is resolved. After
seeing the confirmation message, you can close this windows and go back to install
Windows on GPT disk.
An easier way (without data loss)
You can also change Legacy mode to UEFI without reinstalling Windows if you use the
help of partition software AOMEI
Partition Assistant. It allows you to convert a system disk to MBR or GPT without
affecting OS. In other words, once the conversion is done, you can change to UEFI or
Legacy boot mode and then boot your Windows 10/8/7 without reinstallation.
You can follow the steps below to convert a boot hard drive to GPT without data
loss:
Step 1. Get AOMEI Partition Assistant Pro.
Step2. Right click on the disk that not allowed you to convert because of pagefile
volume, and then select the option “Convert to GPT”.

Step 3. Click the option “Apply” to apply this operation.

Situations like “the operation is not allowed on a disk that contains a pagefile
volume” will never happen with AOMEI Partition Assistant because the whole process
does not interfere pagefile and all the data remain intact.
Besides that, this software can also be used to resize partition, allocate free space,
and convert dynamic disk to basic without data loss.