About Unallocated Space of Copy and Migration Operations

June 23, 2017

When you use AOMEI Partition Assistant, some wizards require that there must be unallocated space in computer disk.

Which circumstance will you see the message?

When you use AOMEI Partition Assistant, some operations require that there must be some unallocated space on disk. In summarize, there are two operations that require an unallocated disk space:

Copy Partition: it is function that copy data and files from one partition to other location. In the process of operating, this wizard requires the destination location must be an unallocated disk space.


Migrate OS to SSD or HDD: it is the function that migrate system drive to from an old HDD to a new SSD or HDD. And the destination SSD or HDD must have an unallocated disk space.


How to create an unallocated space?

In many computers, all space will be allocated to partitions. Hence, how to split an unallocated space out of existing partitions? AOMEI Partition Assistant will help you solve this problem. There are two ways to create an unallocated space.

Way 1: Shrink A Partition

If a partition on disk has free (unused) space, you can use "Resize Partition" to shrink partition, and then the free space on the partition will become unallocated space. Right click any partition (here take E partition for example) which has free space, and select "Resize Partition".


A pop-up window will appear, and drag slider bar leftwards. Then, you can click "OK".


Now you can find that there is an unallocated disk space behind the partition E. To save the change, please click "Apply".


Way 2: Delete A Partition

Deleting a partition can also create an unallocated space. However, before deleting a partition, please remember to backup data or transfer files on the partition to other location. The operation of deleting partition is very simple.

Right click the partition (here take G partition for example) that you want to delete and select "Delete Partition".

Delete Partition

In the pop-up window, there are two ways available to delete partition. To save your time, please tick the option "Delete partition quickly" and click "OK".

Delete Partition

Now you can find that partition G changes into unallocated space. To save the change, please click "Apply".

Delete Partition

Good to know

Why I am unable to copy partition, though I choose an unallocated space? The problem may caused by the size of unallocated soace. There are two methods to copy partition, and each one has some requirement on size of unallocated space.

  • Copy Partition Quickly: only copy the used space of the partition, and supports to resize partition during the copy process (Recommend). If you choose this method, the unallocated space could be smaller than the source partition but MUST be larger than the used space of source partition.
  • Sector by Sector Copy: copy all sectors of the partition to another disk, no matter it is used or not. If you choose this method, please make sure the unallocated space is equal or larger than source partition.