Fixed: 3TB External Hard Drive Suddenly Becomes 746GB Unallocated

April 28, 2018

If you are confused why your 3TB external suddenly becomes 746GB unallocated, you can read this post to know why the 3TB external hard drive not showing the full capacity and how to fix 3TB hard drive only shows 746GB in Windows 10/8/7.

3TB external suddenly becomes 746GB unallocated

Many users have met the problem that 3TB external suddenly becomes 746GB unallocated when they installed their 3TB hard drive into the computer. A friend found a good deal on a WD hard drive with USB 3.0 speeds. Since he did not have a USB 3.0 port on his computer, he wanted to move his files via SATA. But when he removed it from the external enclosure and connected the hard drive straight into the computer, the 3TB external only showed 746GB.

3TB Only Show 746GB

So, what reasons could cause the 3TB external hard drive not showing full capacity?

Why 3TB HDD not showing full capacity?

There are many reasons for why 3TB external suddenly becomes 746GB unallocated.

1. 3TB external suddenly becomes 746GB unallocated is commonly caused by incorrectly configured system settings or irregular entries in the Windows registry. If you are received this error, it means your system operation may have a malfunction. For example, the incorrect or failed installation or uninstallation of software that may have left invalid entries in your Windows registry. Besides, the virus or malware attack, improper system shutdown, unexpected deleting a necessary system file or registry entry, etc, may all cause 3TB external HDD suddenly becomes 746GB unallocated.

2. Format 3TB hard drive in MBR by mistake is another reason for 3TB hard drive not showing full capacity. Hard drives are typically formatted in MBR (Master Boot Record) or GPT (GUID Partition Table). The MBR hard drive will allow you to create a partition of 2TB in size, while the GPT hard drive will allow you to go beyond the 2TB limit. Thus, if you format 3TB hard drive in MBR, it will not show the full capacity.

3. USB or SATA may be a reason for 3TB external hard drive suddenly becomes 746GB unallocated. You may meet the situation as following: when you use your 3TB external hard drive via USB port, it can be recognized without any problem, but when you connect it into your computer with SATA, the hard drive size detection became an issue.

4. A study saying that if you are using the old version of Intel® Rapid Storage Technology (RST) driver, you may receive the 746GB available of the 3TB drive issue.

How to fix the 3TB hard drive only shows 746GB in Windows 10/8/7?

As there are different reasons can cause 3TB hard drive only shows 746GB, here provides you the different solutions for different reasons.

Solution 1: Repair the registry and turn up system settings to restore stability

If your 3TB external suddenly becomes 746GB unallocated because of the incorrectly configured system settings or irregular entries in the Windows registry, you can repair the registry and turn up system settings to restore stability with specific software like Reimage Repair Tool, which will scan and diagnose, then repairs, your PC with patent pending technology that fix your Windows operating system registry structure. It is free to download as well as easy to use, and it is powerful to find malicious items that are hidden on the computer. Do as the following steps:

Install it to your PC, this freeware will automatically start a preliminary scan of your machine to help determine the healthy of your PC.

Reimage Scan

Once the scan complete, it will tell you which areas of your PC are damaged and if a repair is necessary. If it is, click on the Start Repair.

Scan Results

After the repair has finished, your computer should be fixed, and you may need to restart the computer to complete the progress.

Solution 2: Convert MBR disk to GPT

When you format your 3TB drive in MBR by mistake, you need to convert the MBR disk to GPT. And you can use Windows Disk Management tool to do it directly.

First, open the Disk Management by right-clicking My Computer/This PC -> Manage -> Disk Management.

Then, right-click the MBR disk which you want to convert to GPT disk, select Convert to GPT disk to fix 3TB external suddenly becomes 746GB unallocated in Windows 10/8/7.

However, if there is any volume on the MBR disk, you cannot convert it to GPT disk unless you delete all volumes before converting, otherwise, the Convert to GPT disk option may be grayed out. Well, is it possible to convert MBR disk to GPT without data loss?

If you do not want to lose any data on the MBR disk, you can turn to third party software like AOMEI Partition Assistant, which can help you convert MBR disk to GPT without losing data. And you should do as following steps:

Step 1. Free download AOMEI Partition Assistant Standard, install and launch it. Here you can see its main interface contains the basic situations of your hard drives. Right click the MBR disk you want to convert to GPT, and select Convert to GPT Disk in the pop up menu.

Convert to GPT

Step 2. Then, it will remind you that the operation will convert MBR disk to GPT, click OK.

Confirm

Step 3. When you back to the main interface, click Apply ->Proceed to submit the pending operations.

Apply Proceed

After that, you might fix the 3TB not showing full capacity problems.

* If you need to convert system disk from MBR to GPT or vice versa, you should upgrade to AOMEI Partition Assistant Professional edition so that you can convert system disk between MBR and GPT without losing data.

Solution 3: Change the connection way to USB port

For the third reason, one possible explanation is that the device is originally intended to be operated as an USB device, so the controller board is designed to get past that 2TB limit, so without the additional hardware, you didn’t see the entire 3TB as one volume. Thus, you need to connect the 3TB external hard drive via USB port.

Solution 4: Upgrade Intel® Rapid Storage Technology driver

Intel® Rapid Storage Technology is a program developed by Intel. The question is your Intel RST version of 10.0.0.1046 is the culprit behind the 746GB available of the 3TB drive issue. Thus, for 3TB drive support, you should upgrade to Intel® Rapid Storage Technology 10.1 version and newer.

So, here you should download the newest version of Intel’s Rapid Storage Technology drivers from Intel’s site.

After installing Intel® Rapid Storage Technology 10.1 version or newer, the 3TB external hard drive only shows 746GB unallocated in Windows 10/8/7 should be fixed.

Conclusion

Here is the ways for how to fix 3TB external suddenly becomes 746GB unallocated error. And we hope this could be helpful. If you have any questions, or any better solutions, welcome to share at the comment area. Thank you!