Windows Server 2008 convert MBR to GPT

Updated on: November 16, 2019

This article introduces how to convert MBR to GPT in Windows Server 2008 R2 without losing data. Change disk from MBR to GPT with mbr2gpt.exe and NIUBI.

Many Windows 2008 servers have kept running many years, the storage device needs to be replaced no matter you use physical disk or RAID array. The most common issue after upgrading disk is that you cannot use full disk space. For example, on a 4TB disk you can only use 2TB, the remaining space can't be created new or extended to other volume in Disk Management. In this case, you need to change disk from MBR to GPT.

On MBR style disk, you can create maximum 4 Primary partitions, if you want to create more, you also need to convert MBR disk to GPT for Windows 2008 Server.

Cannot convert to GPT in Server 2008 Disk Management

Windows Server 2008 native Disk Management has the ability to convert disk between MBR and GPT, but there must be no partitions in this disk, otherwise these options are grayed out. As you see in my test server, there are drive F: and H: on Disk 1.

When right click this disk, Convert to GPT disk option is greyed out and disabled.

Convert greyed out

After deleting these two partitions, Convert to GPT disk option is enabled.

Convert greyed out

Obviously, the built-in converting option is used for new disk, or there is another large disk to transfer files before deleting existing partitions.

You cannot convert system disk from MBR to GPT in Server 2008 Disk Management, because you can't delete system partition in Windows.

1-click method to convert MBR to GPT

If you want to convert MBR disk to GPT without Operating System, it is very easy and fast with NIUBI Partition Editor.

Download NIUBI and you'll see all disk partitions with structure and other information on the right.

Right click the front of Disk 1 and select Convert to GPT Disk.

Convert to GPT

Then there's pending operation created on bottom left, click Apply to execute.

Apply converting

Watch the video how to convert MBR to GPT disk in Windows Server 2008:

Video guide

How to convert system disk from MBR to GPT

It is much more complicated while converting MBR system disk to GPT in Windows 2008 server, because the boot strategy is different, in addition, your hardware must support booting from UEFI.

To convert system disk, it is suggested to convert with MBR2GPT.exe, which is provided by Microsoft. MBR2GPT works via command prompt, there is no such command included in Windows Server 2008 (and R2), therefore, you need to download from Microsoft.

Steps to convert MBR to GPT with mbr2gpt.exe in Windows Server 2008 (R2):

Step 1: Download Windows 10 setup tool from and select the second option to create installation media with it.

To VMware/Hyper-V virtual server, you may create ISO file. To physical servers, you need to create bootable DVD or USB drive.

Windows tool

Step 2: Restart server and boot from the ISO, DVD or USB flash drive, when it ask you to "Install now", do NOT click it, click "Repair your computer" on bottom left instead. Then click Troubleshoot > Command Prompt in next windows.

mbr2gpt command

Step 3: You just need 2 commands to convert MBR system disk to GPT:

  1. Type cd.. and press Enter.
  2. Type mbr2gpt /convert and press Enter.

In a short time, MBR2GPT reports conversion completed successfully.

Convert successfully

Watch the video how to convert MBR disk to GPT with MBR2GPT command in Windows Server 2008:

Video guide

It is easy to convert with mbr2gpt command prompt, but it costs time to download Windows 10 setup tool and create bootable media.

Precondition of Server 2008 mbr2gpt command prompt

If your disk partition configuration doesn't meet the requirements of MBR2GPT, you'll receive error such as - "Validating layout, disk sector size is: 512 bytes Disk layout validating failed for disk 0", "MBR2GPT: Conversion failed".

Convert error

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 are at most 3 Primary partitions in the MBR partition table.
  3. One of the partitions is set as active and is the system partition.
  4. The disk does not have any Extended/Logical partition.
  5. The BCD store on the system partition contains a default OS entry pointing to an OS partition.
  6. The volume IDs can be retrieved for each volume which has a drive letter assigned.
  7. 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. (The disk won't be converted or modified.) In the list you should pay attention to number 2, 3 and 7.

Check disk partition layout in Disk Management

Press Windows and R together on the keyboard, type diskmgmt.msc and press Enter. Then you'll see disk partitions with structure and other information in Server 2008 Disk Management.

1. Check partition status:

Partition type

From this screenshot, drive D: is Logical partition. In this situation, you need to convert D to Primary partition with NIUBI.

Note: all partitions should be Primary.

2. Check number of partitions:

Partition number

From this screenshot, there are 4 Primary partitions in Disk 0. In this situation, you need to move a partition to other disk with NIUBI.

Note: there should be maximum 3 Primary partitions in a disk.

3. Check partition type:

In Windows Server 2008, the common partition type is NTFS and FAT32, if there are other types of partitions such as EXT2/3 in this MBR disk, it cannot be converted. Check the supported partitions.

In Summary

It is a bit complicated to convert system MBR disk to GPT, but mbr2gpt is the safest tool. If the disk has no Operating System, it is very easy to convert MBR to GPT in Windows Server 2008 R2 with NIUBI Partition Editor. Besides converting disk MBR to GPT, it helps convert partition NTFS to FAT32, convert between Primary and Logical. It also helps copy, shrink, extend, merge, move, defrag, wipe, hide partition, etc.