Convert MBR GPT

Convert MBR disk to GPT on Windows Server 2016

This article introduces how to convert MBR to GPT on Windows Server 2016 with mbr2gpt. Detailed steps to change MBR disk to GPT without data loss.

How to convert MBR to GPT for system disk?

GPT (GUID Partition Table) disk has some advantages than MBR (Master Boot Record) disk, for example: overcome the maximum 2TB partition and 4 Primary partitions limit. That means, you can create larger than 2TB disk and more than 4 Primary partitions in single GPT disk. Hard disk price is much cheaper, single file becomes much larger and there are large amount of files need to be saved to the server. Thus, advantages of GPT are highlighted.

To the servers that runs Operating System on MBR disk for a long time, it can’t be better if you can convert MBR to GPT without starting over or losing data. However, booting from GPT disk is much more complicated than MBR style disk, in addition, your server must support UEFI (difference between UEFI and BIOS)

To convert MBR to GPT on Windows Server 2016 for system disk, you should pay attention. Back up server first and use right tool. There are 3rd party software that has such ability, but few can ensure system bootable. If it failed, you have to waste a long time to restore. Here I’ll introduce how to convert MBR to GPT with Microsoft provided tool – MBR2GPT command prompt.

Tips To Windows 10 1703 and later version, you can run MBR2GPT from Windows command prompt. To the previous versions and Server 2016/2012, you need bootable media to run MBR2GPT from a Windows Preinstallation Environment (Windows PE) command prompt.

Before starting, you should check your disk partition configuration whether fits for the requirements.

Disk Prerequisites

Before any change to the disk is made, MBR2GPT validates the layout and geometry of the selected disk to ensure that:

  1. The disk is currently using MBR
  2. There is enough space not occupied by partitions to store the primary and secondary GPTs:
    • 16KB + 2 sectors at the front of the disk
    • 16KB + 1 sector at the end of the disk
  3. There are at most 3 primary partitions in the MBR partition table
  4. One of the partitions is set as active and is the system partition
  5. The disk does not have any extended/logical partition
  6. The BCD store on the system partition contains a default OS entry pointing to an OS partition
  7. The volume IDs can be retrieved for each volume which has a drive letter assigned
  8. All partitions on the disk are of MBR types recognized by Windows or has a mapping specified using the /map command-line option

If any of these checks fails, the conversion will not proceed and an error will be returned.

Generally speaking, the lists are not an issue but except number 3, 5 and 8.

About number 3, 5 and 8:

In a MBR disk, there could be maximum 4 Primary partitions, or 3 Primary partitions plus an Extended partition. You can create many Logical partitions inside of the Extended partition.

Right click Windows on bottom left corner of the screen and select Disk Management, and then you’ll see how many partitions in a disk. It doesn’t matter if you use single physical disk or RAID array virtual disk.

There are 3 Primary partitions in Disk 0, so converting this MBR disk to GPT is supported.

But if there are 4 Primary partitions or even one Logical partition in Disk 0, you can’t convert this MBR disk to GPT on Server 2016.

If there are other types of partitions such as EXT2/3 in this MBR disk, it cannot be converted. Check the supported partitions.


Steps to convert MBR to GPT on Server 2016 with MBR2GPT

Step 1 Download and install NIUBI Partition Editor to expand the System Reserved partition.

Important: For Windows to remain bootable after the conversion, an EFI system partition (ESP) must be in place. MBR2GPT will shrink the System Reserved partition first, if there is not enough free space in it, MBR2GPT will shrank the OS C drive. In that case, the EFI partition will be created on the right side of C drive, which cause serious issue, for example: C drive cannot be extended forever.

EFI partition

Once MBR to GPT conversion is completed, this operation can’t be undone, so to avoid this issue, you’d better expand the System Reserved partition first.

Watch the video how to do this:

Step 2 Download Windows 10 setup tool from and select the second option to create installation media with it.

Step 3 Burn to USB disc, DVD or build ISO file and burn later with your own tools. (Note: Use blank media or transfer files before burning.)

Step 4 Boot from USB or DVD, when it ask you to “Install now”, do NOT click it, click “Repair your computer” on bottom left instead.

Click Troubleshoot in the next window.

Click Command Prompt in the next window.

Step 5 Copy, paste and execute the two commands one by one: (see full Syntax and options)

mbr2gpt /convert

/validate – Instructs MBR2GPT.exe to perform only the disk validation steps and report whether the disk is eligible for conversion. If validating failed, you cannot continue converting.

/convert – Instructs MBR2GPT.exe to perform the disk validation and to proceed with the conversion if all validation tests pass.

/disk:<diskNumber> – Specifies the disk number of MBR disk to be converted to GPT. If not specified, the system disk is used, so this option is used here.

Restart server and boot to UEFI, as you see, disk 0 is converted to GPT and the EFI system partition is created on left side of C drive.

Converted to GPT

How to convert MBR to GPT for non-system disk?

To convert MBR to GPT on Windows Server 2016 for non-system disk, it is extremely easy and fast. Simply run NIUBI Partition Editor, select the MBR disk and convert. Watch the video:

Besides converting MBR disk to GPT, NIUBI Partition Editor helps you convert partition between Primary and Logical, convert NTFS to FAT32 without losing data. It helps you shrink, extend, move, merge, copy, wipe partition, etc.