Solved: Unable to Convert a Disk to GPT in Windows Server

In the ever-evolving landscape of information technology, Windows Server remains an indispensable platform for businesses and organizations around the world. Its versatility and robust capabilities have made it a go-to choice for hosting critical services and applications.

However, even the most reliable systems encounter occasional challenges. One such challenge is when Windows Server is unable to convert a disk to GPT (GUID Partition Table). This issue can be a significant roadblock, particularly when trying to leverage advanced storage features or working with larger disk capacities.

Unable to convert my disk to GPT in Windows Server 2012 R2

“I have Windows Server 2012 R2 installed on my machine and I want to convert my 3TB external hard drive to GPT so that I can make full use of it. But I found the option of 'Convert to GPT Disk' greyed out when I tried to change my hard drive from MBR to GPT partition style via Disk Management.

Then, I tried to make conversion via Diskpart utility and only got the "Virtual Service error: The specified disk is not convertible. CDROMs and… “message. What should I do when encountering Windows Server unable to convert a disk to GPT via Disk Management or Diskpart? Is there any advice?”

How to solve can’t convert a disk to GPT in Windows Server?

Compared with the MBR partition style, GPT supports a hard drive beyond 2 TB and allows you to create up to 128 primary partitions. To make unallocated space on a hard drive over 2TB or to create more primary partitions on a hard drive, converting disk from MBR to GPT is necessary.

However, if the disk needs to be converted to hold partition(s), you can encounter the errors mentioned above and won’t be able to convert the MBR disk into GPT. To fix this problem, you can delete all partitions on the disk that going to be converted and then convert it. Have a look at the detailed steps.

The First stage (omissible): Backup volume via Windows Server Backup

Since removing the partition will make data loss, you can backup volume to a local disk or removable device at first. If there is no necessary data saved on this disk, you can skip it.

Step 1. In the Search Box, type “windows server backup” to access the Windows Server Backup utility.

PS.: If you have not used this function, you need to install (Server Manager\Features) it in advance.

Step 2. Click Backup Once Wizard and follow it to execute backup settings.

The second stage: Delete partitions all partitions & convert a disk to GPT

After backing up the wanted files, you can remove partitions from the disk and convert a disk from MBR to GPT.

Option 1. Delete partition and convert disk via Disk Management

If there is only one operation on the disk, deleting the partition and making conversion via Windows Server Disk Management is not a bad choice.

Step 1. Press “Windows + R” simultaneously, type “diskmgmt.msc” and hit Enter key to open Disk Management.

Step 2. Right-click the partition that you need to delete and choose “Delete Volume...”.

Step 3. After deleting all partitions on the disk that’ll be converted into GPT, you can right-click the disk and choose “Convert to GPT Disk”

The whole conversion process will be completed within a few seconds. After conversion, you can create a partition with the unallocated space and restore backed-up data.

Option 2. Delete partition and convert disk via Disk Management

When there are multiple partitions on the disk and it is a lit bit bothering to delete partitions one by one, you can delete all partitions and convert a disk to GPT via Diskpart utility.

1. Press "Windows + R" at the same time, input “diskpart” and hit Enter.

2. Run commands given below:
▪ list disk
▪ select disk n (n refers to the number of the disk that you need to convert)
▪ clean
▪ convert gpt

When you are prompted that Diskpart successfully converted the selected disk to GPT format, you can type “exit” and hit Enter key.

How to easily convert a disk to GPT without data loss in Windows Server?

To convert disk into GPT in Windows Server effortlessly, it is recommended to employ a third-party partition manager – AOMEI Partition Assistant Server. It allows you to convert MBR disk that contains data without deleting any partition in Windows Server 2025/2022/2019/2016/2012(R2). And it has a very modern and concise graphic user interface, enabling you to handle it rather easily. Now, see how to convert MBR to GPT without data loss in Windows Server.

It's available to free download its demo version to have a try

Step 1. Ensure that the MBR disk needs converting is connected to your machine well; install and run AOMEI Partition Assistant Server. Right-click the MBR disk that and select “Convert to GPT”.

Step 2. In the pop-up window, click “OK” to continue the operation.

Step 3. In the main interface, click “Apply” > “Proceed” to perform the operation.

★PS.:

 If you need to convert the system disk into GPT and boot from it, please change Legacy to UEFI after the conversion.

 It is also available to convert GPT to MBR without data loss in Windows Server via AOMEI Partition Assistant Server.

Conclusion

When your disk owns partitions, Windows Server is unable to convert the disk to GPT directly using Disk Management or Diskpart utility. If you insist on doing so, you'll have to delete partitions on the disk at first.

Or you can choose to use AOMEI Partition Assistant Server to convert a disk from MBR to GPT without deleting any partition. What's more, you can also use it to clone Windows Server hard drive, convert dynamic disk into basic without data loss, and more.