Solution - Cannot Extend C: Drive in Windows Server 2012 R2

Updated on: July 5, 2022

C drive low disk space is common issue in Windows 2012 server. When it happens, nobody likes to waste a long time to recreate partitons and restore. The same with previous version, there's "Extend Volume" function in Disk Management. Some people tried to extend C drive with this native tool but failed, because "Extend Volume" option is grayed out. In this article, I'll introduce why you cannot extend C drive in Windows Server 2012 Disk Management and what to do when you are unable to extend C drive in Server 2012 R2.

Why can't extend C drive in Server 2012 Disk Management

There are 2 native tools to help extend partition in Server 2012 - Diskpart and Disk Management. Diskpart is a command line tool including "Extend" and many other commands. Disk Management has "Extend Volume Wizard" with graphical interface. Although these tools work in different way, they have same restrictions when shrinking and extending partition. To better explain the reasons, I only show you with GUI Disk Management.

Reasons why cannot extend system partition C in Windows Server 2012 r2:

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 "Unallocated" space on the same disk. If you did not delete or shrink other volume to get such space, of course you cannot extend C drive.

The serious issue is that you still cannot expand C drive in Server 2012 Disk Management after shrinking other partitions. As you see in my server, Extend Volume is disabled for C drive after shrinking D.

This is because:

  • Unallocated space can only be made on the right while shrinking partition with Disk Management.
  • Unallocated space can only be added to the left contiguous partition.

2. Limitations of MBR disk

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

In most of servers, the adjacent drive D is used for programs or some services, so you cannot delete it.

If the contiguous partition D is Logical , you still cannot enlarge C drive even after deleting D.

This is because:

On MBR disk, there are maximum 4 entries in master boot record sector. So you can create maximum 4 Primary partitions, or 3 Primary plus an Extended partition. If you want to create more partitions, they must be created as Logical inside of the Extended partition.

As you see in my test server, disk space of D drive is shown as Free after deleting, "Extend Volume" is still disabled for C drive.

Cannot extend

What to do when unable to extend C drive in Server 2012 r2

With NIUBI Partition Editor, this problem can be solved easily. It is able to combine Unallocated space to either contiguous partition with 1 step, no matter it is Primary or Logical. 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

Steps when you cannot extend C: drive in Windows Server 2012 R2 after shrinking D/E:

Step 1: Right click drive D: and select "Resize/Move Volume", drag middle  of this partition 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 drive C: 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 operate:

Video guide

What to do when cannot extend C drive to another disk

No disk partitioning software can extend a partition with free space in other separated disk. If there is no available space on the same disk, you can clone disk to a larger one with NIUBI Partition Editor, and then expand C drive (and other volumes) with extra disk space.

Follow the steps in the video:

Video guide