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.
So, what reasons could cause the 3TB external hard drive not showing full
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
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
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
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
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.
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.
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
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
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.
Step 2. Then, it will remind you that the operation will
convert MBR disk to GPT, click OK.
Step 3. When you back to the main interface, click Apply->Proceed to submit the pending operations.
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
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
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!