Cannot/unable to extend C drive on Windows Server 2012

by John, Updated on: July 4, 2020

This article explains why you cannot extend C drive in Windows Server 2012 R2, and what to do when Disk Management is unable to extend C drive partition.

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, or 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 functions in Disk Management, not all partitions can be resized. Many people feedback that they can't extend C drive in Server 2012 Disk Management, even after shrinking the adjacent D drive.

Why cannot extend C drive in Windows Server 2012 DM

Both Shrink and Extend Volume support NTFS partition only, however, it is not an issue to system partition C, because system partition is formatted with NTFS by default. The most common reasons why you are unable to extend C: drive 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.

1. No adjacent Unallocated space on the right

Extend volume disabled

The size of a physical disk is fixed, thus before extending C drive, there must be free Unallocated space. If you did not delete or shrink other volume to get such space, of course you cannot extend C drive with any tool.

Obviously, it is better to get Unallocated space by shrinking a volume, because you won't lose files in it. The problem is that you still cannot expand C drive after shrinking D or other partitions. As you see in my server, Extend Volume is disabled for C drive after shrinking D.

This is because:

  • Extend Volume only works when there's adjacent Unallocated space on the right and on the same disk.
  • Shrink Volume can only make Unallocated space on the right while shrinking a partition.

The Unallocated space shrunk from D: drive is nonadjacent to C drive, so Extend Volume greyed out.

2. The right contiguous partition is Logical

This issue only exists on MBR disk, you can ignore this section if you use GPT disk.

Because Windows Server 2012 cannot extend C drive by shrinking other volume, some people are wondering if it is possible to delete D drive to get the contiguous Unallocated space. Yes, it works if D is a Primary partition. If it is Logical drive, you still cannot extend C drive for Server 2012 after deleting.

This is because:

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 all Logical partitions should be 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.

Cannot extend

As you see in my test server, disk space of D drive is shown as Free after deleting. It is still part of the Extended partition, so Extend Volume doesn't work.

If you want to convert this Free space to Unallocated, you must delete all other Logical drives and the entire Extended partition. Obviously, it's not a good idea.

What to do when unable to expand C drive

With NIUBI Partition Editor, this problem can be solved easily. It is able to combine Unallocated or Free space to either contiguous partition with 1 step. When the Unallocated space is nonadjacent, it is able to move it and then combine to other partition on the same disk.

Download it and you'll see the main window with disk partition structure and other information. There is 20GB Unallocated space that is shrunk from D drive via Disk Management.

NIUBI Partition Editor

Follow the steps when Windows Server 2012 is unable to extend C drive after shrinking D:

Step 1: Right click D: drive and select "Resize/Move Volume", drag middle position towards right in the pop-up window:

Move rightwards

Then Unallocated space is moved to the left side.

Move Unallocated space

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

Expand C drive

Then Unallocated space is merged into C: drive.

Unallocated add to C

Step 3: Click Apply on top left to take effect. (The operations before clicking Apply just work in virtual mode.)

Watch the video how to move Unallocated space and add to C drive:

Video guide

Because of the limitations of Shrink and Extend Volume, you can't extend C drive in Windows Server 2012 Disk Management, so 3rd party tool is needed. Better than other software, NIUBI Partition Editor has unique 1 Second Rollback, Virtual Mode and Cancel-at-well technologies to protect your system and data. Besides shrinking, moving and extending partition, it helps you do many other operations.