By AOMEI / Last Updated October 12, 2019

In Windows Server 2012 (R2), resizing partitions or re-partitioning a hard drive has become much easier than in previous Windows versions such as Windows Server 2003 and 2000. Both Windows Server 2012 and 2012 R2 are equipped with an improved Disk Management tool, which enables you to change partition size by shrinking or extending volume, and create new partitions from unallocated space, etc.

However, there are still some shortcomings that will require you to turn to third-party disk partition management utility and one of the shortcomings is the option to extend volume greyed out even there is unallocated space on the same disk.

Example 1:

Let's say you have a Windows Server 2012 R2 with C: and D: drives on the same disk. With more and more programs installed and data added, the C: drive is running out of free space but D: drive has a lot of free space. You freed up 100 GB unallocated space from the D: drive using the Disk Management "Shrink Volume" option and that needs to be added into C: drive. But the "Extend Volume" option on the C: drive is grayed out and disabled.

Example 2:

Let's say you have a server machine with 3x500GB disks configured as a RAID 5 array, which was partitioned into C: drive for Windows Server 2012 R2 installation and D: drive for data. Now both C: and D: drives are almost full. You successfully add another 500GB disk into RAID 5 and Disk Management sees the additional disk space as unallocated and it is directly behind D: drive. The "Extend Volume" option is available only on D: drive but greyed out on C: drive.

Why "Extend Volume" greyed out in Windows 2012?

The Disk Management "Extend Volume" only works with contiguous unallocated space behind the target partition you want to extend, which means that the unallocated space must immediately locate to its right side. If not, Extend Volume will be greyed out and hence not available.

Windows 2012 Disk Management Extend Volume Greyed Out

Note: sometimes you still find that "Extend Volume" is greyed out even though an unallocated space is contiguous behind the target partition. This is caused by disk partition style. To solve this problem, you need to convert MBR to GPT disk for using unallocated space beyond 2TB.

Extend Volume Greyed Out 3TB

Workaround for extend volume greyed out

Step 1: Backup the partition (here is D:) behind the target drive (here is C:) you want to extend. Right-click on the D: partition and select "Delete Volume" in the drop-down list.

Delete Volume

Step 2: Once you have D: partition delete, it will turn into an unallocated space and be automatically merged with other unallocated space that is next to it if have. Now you can right-click on C: drive and "Extend Volume" option is available.

Extend Volume

Step 3: In the "Extend Volume Wizard" window, you can input the amount of space in MB to add into C: drive. To finalize the modifications, click "Next".

Extend Volume Wizard

You can use the rest of unallocated space if have to re-create D: partition and then restore data.

Solve extend volume greyed out simply and quickly

Generally speaking, third-party applications work the same as Windows Server 2012 R2 built-in Disk Management tool. The difference is that they provide more features and are much more flexible. For example, you can extend a volume regardless of where the unallocated space locates. Here recommend AOMEI Partition Assistant Server.

Step 1. Install and launch it. Right-click on the partition (here is C: drive) you want to extend and select “Merge Partitions” in the drop-down menu.

Merge Partitions

Step 2. In the pop-up window, check the box before unallocated space which means that the unallocated space will be added into C: drive. And the click “Next” button to continue.

Choose Unallocated Space

Step 3. Now you can preview the unallocated space behind D: partition is added into C: drive. To make the changes come into effect, click “Apply”.



  • If you want to extend a volume but there is no unallocated space on the same disk, please refer to move free space from one partition to another.

  • This guide also applies to all versions of Windows, including Windows Server 2003, 2008, 2011, 2016, 2019 and Windows 10, 8.1, 8, 7, Vista, XP.