Convert MBR disk to GPT on Windows Server 2016

Updated on: November 16, 2019

This article introduces how to convert MBR to GPT in Windows Server 2016 without data loss, change MBR disk to GPT with mbr2gpt.exe and partition editor.

GPT (GUID Partition Table) disk has many 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 partition and more than 4 Primary partitions in single GPT disk. It is common to use over 10TB disk (hardware RAID array) for a server, if you do not convert MBR disk to GPT, the rest disk space will be shown as Unallocated and it can't be used to create new volume or expand to other volume.

To a MBR disk that already has data or Operating System, it can't be better if you can convert it to GPT without losing data. To a MBR disk for data only, only several clicks are needed with a MBR to GPT disk converter. But to system disk, it is more complicated, because the boot stratagem is different. This article introduces detailed steps to convert MBR to GPT on Windows Server 2016 without data loss for both data and system disk.

How to convert MBR to GPT for non-system disk

  1. Download NIUBI Partition Editor, right click the front of the MBR disk and select "Convert to GPT Disk".
  2. Simply click Yes to confirm, then a pending operation is added.
  3. Click Apply on top left to execute, done. (All operations before clicking Apply only work in virtual mode.)

Watch the video how to convert MBR disk to GPT in Windows Server 2016:

Video guide

As you see, it is very easy and fast to complete converting.

How to convert system disk with MBR2GPT command

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 100% system bootable. If it failed, you have to waste a long time to restore. Here I'll introduce how to convert MBR disk to GPT with Microsoft provided tool - MBR2GPT.

MBR2GPT.exe is running from command prompt. On Windows Server 2019 and Windows 10 (1703 and later versions), you can convert MBR to GPT with this command in Windows. But to run mbr2gpt on Windows Server 2016, you need to create bootable media with Windows Preinstallation Environment (Windows PE).

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

Disk partition prerequisites

Before any change to the disk is made, MBR2GPT validates the layout and geometry of the selected disk, if any of these checks fails, the conversion will not proceed and an error message will be returned.

  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 and 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 this MBR disk are recognized by Windows.

In general, you just need to pay attention to number 3, 5 and 8.

Preparation for converting

Note: If there are more than 3 partitions, or even one Logical partition, or any non-support partition such as EXT2/3 in the disk, you can't convert MBR disk to GPT in Windows Server 2016.

If your disk partition configuration doesn't meet the requirements, when MBR2GPT command check the geometry, it will reports error - "Validating layout, disk sector size is: 512 bytes Disk layout validating failed for disk 0", "MBR2GPT: Conversion failed".

Partition layout

In most of Windows 2016 server system disk, there are System Reserved, C: (for OS) and D drive. If all these 3 partitions are Primary, you can convert this disk successfully.

  • If partition D is Logical, follow the step to convert it to Primary (without data loss).
  • If there is fourth partition such as E, move it to other disk no matter it is Primary or Logical.
  • If there are any Windows non-support partition, move files to other place and delete this partition.

Now, you can convert MBR disk to GPT for Server 2016, but before this, there's an important step.

Pay attention to EFI partition

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 causes serious issue - C drive cannot be extended forever by either Windows native or 3rd-party software.

In the command prompt, it shows clearly the steps what MBR2GPT do when converting MBR disk to GPT. As you see, MBR2GPT first try to shrink the system reserved partition, it can't be done, so it shrink the OS partition C instead.


Before converting MBR disk:

Before converting

After converting to GPT disk:

After converting

As you see, 100MB EFI system partition is created behind C drive after converting Disk 0 to GPT. When right clicking it, all options are grayed out.

To avoid this serious issue, you should expand the system reserved partition before converting. Note: this operation requires server rebooting, because when shrinking the OS partition C, the start position will be changed.

Download NIUBI Partition Editor and follow the method in the video to expand the System Reserved partition (it's enough to 1GB):

Video guide

Steps to convert MBR to GPT on Server 2016

After the preparation is ready, it is very easy and fast to complete converting MBR system disk to GPT, follow the steps below.

Step 1: Download Windows Server 2019 ISO and create bootable DVD disc or USB flash drive with Windows built-in or third-party tool.

Step 2: Boot from this bootable media, simply click Next in first Windows Setup window, then click Repair your computer on bottom left corner of next window.

Setup window

Repair computer

Step 3: Click Troubleshoot in next window, then click Command Prompt.


Command Prompt

Step 4: Just input 2 commands to complete converting.

  1. cd..
  2. mbr2gpt /convert

Within several minutes, this MBR disk is converted to GPT. As you see, this time MBR2GPT shrink the system reserved partition successfully. Restart server and boot to UEFI, disk 0 is converted to GPT and the EFI system partition is created on left side of C drive.

MBR2GPT command

Convert successfully

In Summary

It is very easy and fast to convert MBR data disk to GPT with NIUBI Partition Editor. To ensure system bootable after converting MBR system disk to GPT, it is suggested to run Microsoft provided MBR2GPT command tool. Before converting, modify your disk partition if it doesn't meet the requirements. Remember, it is very important to expand the system reserved partition before converting MBR disk to GPT on Windows 2016 Server.

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 also helps you shrink, extend, move and merge partitions to optimize space usage, clone entire disk or single partition to migrate Operating system and data, create, delete, format, convert, defrag, hide partition and much more.