Cannot extend C: drive in Windows Server 2012

Updated on: November 16, 2019

This article introduces why cannot extend C drive in Windows Server 2012 Disk Management, and what to do if unable to extend system partition for Server 2012.

Why can't extend C drive via Diskpart or Disk Management

Many server administrators want to resize and extend partition after running the server for a period of time, the typical issue is that system C drive running out of space. To help extend disk partition without losing data, Microsoft provides two native tools - Diskpart and Disk Management.

Diskpart is command line tool including Extend and many other commands. Disk Management works with graphical interface. Both Diskpart cmd and Disk Management works under restricted condition, therefore, many people feedback that they are unable to extend C drive.

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

Diskpart and Disk Management work in different way, but they have nearly the same restrictions. To better explain the reasons, I only show you with GUI Disk Management.

1. No adjacent Unallocated space on the right

Extend volume disabled

The size of a hard 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.

The serious issue is that you still cannot expand C drive 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 with either native tool.
  • Unallocated space can only be added into the left contiguous partition.

2. Birth defect 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 D is Logical partition, you still cannot enlarge C drive even by deleting D.

This is because:

In MBR disk, there are maximum 4 entries in master boot record sector. 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. It is still part of the Extended partition.

Cannot extend

Only Unallocated space can be combined to the left contiguous (Primary) partition via Disk Management. If you want to convert the Free space to Unallocated, you must delete all other Logical and the entire Extended partition.

You can add this Free space to C drive with Diskpart.

What to do if unable to extend C drive with native tools

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, 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 in 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 to fix the issue that can't extend C: drive in Windows Server 2012:

Step 1: Right click drive D: 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 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 fix Extend Volume greyed out issue in Windows 2012 server:

Video guide

Solution - cannot extend C drive to other disk

No disk partitioning software can extend a partition with free space in other separated disk. If there is no available space in a disk, you can copy it 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