By AOMEI / Last Updated May 15, 2020

About the unallocated space after Windows 10 upgrade

After free upgrade to Windows 10 from Windows 7/8.1, mysteriously they lost a partition, which is shown as unallocated space in Disk Management. Nowadays, many users have installed large hard drive over 2TB in the computer in order to store all the important stuff. If you are using over 2TB hard drive, the space beyond 2TB becomes unallocated space, leaving you no options to utilize this space. If you look deep into it, you may find out that this hard drive has been miraculously converted to MBR partition table from GPT. MBR disks support up to 2TB capacity, which is why you cannot use the unallocated space to create a new partition or merge into other partitions on the same disk. If you hard drive is less than 2TB and you still lost one partition, that is because your MBR disk has 4 primary partitions, and Windows 10 created a recovery partition by shrinking the C drive during the upgrade. On MBR disk, there can only be at most 4 primary partitions, so the last partition on your hard drive get deleted.

How to reclaim space after Windows upgrade?

If your hard drive was GPT previously, you can also convert MBT to GPT without data loss by using third party software, such as AOMEI Partition Assistant.

To convert MBR to GPT without affecting OS:

1. Download and run AOMEI Partition Assistant Professional.

2. At its main interface, you can see the all the disks and partitions status. Right click on the disk that lost space and select “Convert to GPT disk”.


4. Then you can right click on the unallocated space and create a new partition or you can merge the unallocated space to other partitions by using “Merge Partitions” function.

5. After that, click “Apply” to save all these changes.


All these operation can be undone before you click the “Apply” button, and the process will be complete in AOMEI PreOS mode after a reboot. If your hard drive was MBR, you can delete the recovery partition by creating a Windows 10 recovery drive. Also, you can still use AOMEI Partition Assistant to directly create a logical partition with the unallocated space. It will automatically convert the last partition on the hard drive into logical partition.

How to avoid windows 10 unallocated space being generated?

If your hard drive is GPT, which contains an EFI system partition and MSR partition, then your computer has UEFI support. Most of the UEFI computers support compatible Legacy BISO based boot mode which allows you to boot from an MBR disk. If you enable both UEFI and Legacy mode, Windows may mistakenly take Legacy mode, and then convert your hard drive to MBR. Therefore, to prevent this, you can make sure you only use UEFI mode by disable Legacy mode.

If your hard drive is MBR, you can convert one of your partition to logical partition, then should not lose a partition during the Windows 10 upgrade. There is also another way to avoid the problem that a partition become unallocated. Windows 10 recovery partition upgrade will only be created when it detects the system reserved partition or recovery partition (if you have one) has insufficient space. Therefore, you can also extend the system reserved partition before upgrade to Windows 10.

No matter what situations you are in, you can use AOMEI Partition Assistant to help you manage the unallocated space after Windows 10 upgrade problem. Besides, it also has many powerful featuers including OS Migration, Dynamic Disk Converter, and Windows 8/10 to Go Creator.