Cannot extend volume

Cannot/unable to extend C drive on Windows Server 2012

This article introduces why you are unable to extend C drive with Windows Server 2012 (R2) Disk Management, and what to do when it cannot extend C drive volume.

About Extend Volume in Disk Management

Disk partitions are allocated while installing Operating System, but sometimes you need to change the partition size. For example: a volume is too large and you need to shrink it, system C drive is getting full and you want to expand it. To help resize partitions without reinstalling OS or losing data. Microsoft provides advanced Shrink and Extend Volume feature in Disk Management.

However, no matter you use DiskPart command prompt or the GUI Shrink/Extend Volume functionalities, not all partitions can be shrank or extended. Many people feedback that they can’t extend C drive in Server 2012 Disk Management, even if shrinking the adjacent drive D.

Why cannot extend C drive in Server 2012 DM

Both Shrink and Extend Volume support NTFS partition only, however, it is not an issue to system C drive in most cases. The most common reasons why you are unable to extend volume C on Windows Server 2012 include:

  1. No contiguous Unallocated space on the right side
  2. The adjacent drive (D:) is Logical partition.

I’ll explain one by one.

Reason 1 No right adjacent Unallocated space

Extend Volume can only expand the drive with contiguous Unallocated space on its right side, otherwise, when you right click this drive Extend Volume is grayed out.

A 512GB disk can’t be increased to 1TB, so before extending a volume you must delete or shrink another one to get Unallocated space. Obviously, it is better by shrinking a volume, because you won’t lose files in the partitions. However, the built-in Shrink Volume can only shrink a partition to the left and produce Unallocated space on the right.

As you see, the 20GB Unallocated is non-adjacent to drive C after shrinking D, of course I can’t extend C drive on Server 2012.

Cannot extend C

Reason 2 Partition D is Logical

Because Shrink Volume cannot produce Unallocated space on the left side, some people wondering if it is possible to delete the contiguous drive D, so the disk space will to converted to Unallocated and next to C drive. Yes, it works if drive D is a Primary partition.

As you see, Extend Volume is enabled for C drive after deleting D.

Caution Do not do this if you installed programs or there are Windows services running from D, because they’ll stop working after deleting D.

Extend available

However, if drive D is Logical, you still cannot extend C drive for Server 2012 after deleting D.

To show you this reason, I recreate D as Logical and then delete it:

Logical D

As you see, disk space shows as Free instead of Unallocated, and Extend Volume is unavailable to C drive.

Extend unavailable

In a MBR style hard disk, you can create maximum 4 Primary partitions, or 3 Primary partitions plus an Extended partition. Extended partition works like a container and other partitions can only be created as Logical inside of it.

Free space deleted from a Logical partition can’t be extended to any Primary partition. Meanwhile, Unallocated space deleted from a Primary partition can’t be extended to any Logical partition.


  • Right click the Free space and select “Delete Partition”, it will be converted to Unallocated.
  • If partition E is also Logical, you have to delete partition D, E and then entire Extended partition one by one, then the disk space will be converted to Unallocated next to C drive.
  • In GPT style disk, all partitions are created as Primary.

What to do when unable to expand C drive

It seems to be a bit complicated, but to solve this problem, it is VERY easy. I’ll show you corresponding solutions one by one.

Solution 1 Can’t extend volume C on Server 2012 because of no right adjacent Unallocated space:

Step 1 Download NIUBI Partition Editor, right click drive D and select “Resize/Move Volume”.

Partition Editor

Drag the middle position rightwards in the pop-up window.

Move partition D

Unallocated space is moved from right of D to the left side.

Drive D moved

Step 2 Right click C drive and select “Resize/Move Volume” again, drag right border rightwards in the pop-up window.

Extend C drive

Unallocated space is combined into C drive.

C drive extended

Solution 2 Can’t extend C drive for Server 2012 because D is Logical

Watch the video:


  • No matter the adjacent drive D is Logical or Primary, you can follow the steps in the video to shrink it and then add Unallocated space to C drive.
  • If there is not plenty of free space in drive D, you can shrink any non-adjacent volumes.

Because of the limitations of Shrink and Extend Volume, you can’t extend C drive volume in Windows Server 2012 (R2) Disk Management, so 3rd party tool is needed. Better than other software, NIUBI Partition Editor provides unique 1 Second Rollback, Virtual Mode and Cancel-at-will technologies to ensure system and data intact. Thanks to the Hot-Resize technology and special File-moving algorithm, it is also much faster.