By Teresa / Last Updated February 17, 2020

4TB hard drive only shows 2TB in Windows?

After migrating from 1.5TB hard drive to 4TB hard drive, you might find that 4TB hard drive shows as 2TB or 1.6 TB in Disk Management, and the rest space showing unallocated space after cloning. Right click on the unallocated space, you will find all options except Parameters and Help are grayed out. So you cannot create new volume with the unused space. If you want to extend volume on the primary partition, you would possibly get error message as follow: Only the first 2TB are usable on large MBR disks. Cannot create partitions beyond the 2TB mark, nor convert the disk to dynamic.

There would be 4TB hard drive unallocated after installing if you just bought it. You are likely to making use of only 2TB of that big size hard disk when you want to create new partitions. Why would this happen? And how can you make full use of the large disk?

Why 4TB hard drive shows up as 2TB?

The answer is the partition table of the 4TB hard drive must be MBR, which supports only up to 2 TB data density. The partitions were organized using a scheme called the Master Boot Record (MBR) which is the most widely used partition scheme in personal computers. However, the MBR scheme was designed for early computers and not flexible enough to accommodate newer disk configurations.

The GUID Partition Table (GPT) was introduced as part of the Unified Extensible Firmware Interface (UEFI) initiative. GPT provides a more flexible mechanism for partitioning disks than MBR partitioning scheme that was common to PCs. Namely, it can support a hard disk that is larger than 2TB. So you need to convert the 4TB hard disk drive with unallocated space from MBR partitioning scheme to GPT.

Fix unallocated space on 4TB hard drive by converting to GPT

From above, we know the solution to unallocated space on 4TB hard disk is to convert the partition style to GPT. Well, how to convert MBR to GPT? This can be done via Windows built-in Disk Management and DiskPart.exe tool. But both of them require you to delete all existing partitions on the disk first, then you can successfully convert it to GPT. Otherwise, you will encounter Convert to GPT Disk greyed out issue or receive virtual disk service errors.

So, you can turn to reliable and powerful partitioning software since you already have contents on the 4TB hard drive and don’t want to lose everything on it. For this task, AOMEI Partition Assistant Standard is highly recommended. This free partition manager is compatible withWindows 10/8/7, allowing you to convert 4TB MBR disk to GPT without losing data/deleting partitions. It has a user-friendly interface, download it to have a try.

Convert 4TB MBR to GPT without data loss in Windows

Step 1. Install and launch Partition Assistant Standard. Right click the hard drive you want to convert and select Convert to GPT Disk.

Convert 4TB to GPT

Step 2. Click OK in the pop-up window to confirm the operation. Now you will find the partitioning scheme has turned into GPT. Don’t forget to click Apply to execute this task.


Step 3. Click Apply after your confirmation.

4TB Apply

For system boot disk conversion between MBR and GPT styles, to guarantee system bootable, you need to enter BIOS and change the boot settings after the conversion is completed.
For conversion between MBR and GPT disks on Laptop, please make sure the power supply is sufficient.
To ensure the data is consistent, do not abnormally terminate the program during the conversion process.
If you want to convert system disk to GPT without data loss, please upgrade to AOMEI Partition Assistant Professional.


The conversion from MBR to GPT could be done within only three steps. After the conversion, you are able to allocated unallocated space on 4 TB hard drive to other primary partitions or create new volume with it. You can learn more use of the unallocated space by referring to Recover External Hard Drive Unallocated Space in Windows 7/8/10. From the snapshots you may know AOMEI Partition Assistant is able to help you solve many other practical problems, like convert FAT32 file system to NTFS in Windows 7, migrate Windows OS from one SSD to another SSD, and create bootable USB drive.

Besides, AOMEI Partition Assistant Professional and AOMEI Partition Assistant Server, as the advanced editions, are embedded more powerful features. For example, you can allocate free space directly from data partition to system drive and migrate OS from GPT disk to GPT disk using Professional. The latter one is designed for Windows Server users.