Convert MBR Partitioned Drives to GPT

KB ID 0001407


I got asked if I’d ever had to do this today, I vaguely remember having this problem in the past, but I can’t remember how I solved it. You set the ‘Partition Table Type‘ on a  disk in Windows, when the drive is first initialised, like so;

And the default is MBR, so that usually gets ticked, the problem is MBR only supports disks up to 2TB in size. Now if it’s just a new disk, with no partitions on it, you can simply change it;

But if it’s got a partition on it, (and probably some live data) you cant!

The Microsoft solution is to delete the partitions and create a new one, which can be a little time consuming, especially if you have live data on it! So can you convert it to GPT Live with no data loss? 


Yes! As usual, make sure you have a decent backup first, and if you are using a virtual environment, you can snapshot the virtual machine before hand, (I tested this in the lab, by taking a snapshot, converting a drive from MBR to GPT, then reverting to the snapshot, and it flipped back to MBR with no loss of data). 

You need to know what disk number Windows has assigned to the drive, in disk management right click the drive, and select properties.

Download and extract gptgen-1.1 then run the following command;

gptgen.exe -w \\.\\physicaldisk1

Note: Where ‘1‘ is the disk number you took note of above.

That’s it done! In ‘disk management’ you will need to ‘Rescan Disks’ to see the change.

In the unlikely event that something exploded, you can ‘roll-back‘ to your snapshot.

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Author: PeteLong

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