Just like previous versions, Windows Server 2016 features the native "Extend Volume" function within its built-in Disk Management tool. When the C drive runs low on space, many administrators try to increase C drive space by expanding the partition, only to find that the option fails. They cannot extend the volume in Server 2016 using Disk Management because the Extend Volume option is greyed out. This article explains why Disk Management is unable to extend volumes in Windows Server 2016 and shows you how to resolve this problem easily.
1. Why You Cannot Extend Volume in Server 2016 After Shrinking
A physical 500 GB disk cannot be increased to 1 TB (with the exception of virtual disks). Therefore, before extending a partition, you must first delete or shrink another volume to obtain unallocated space. Disk Management includes a built-in Shrink Volume function to decrease partition size and generate unallocated space. Although many users successfully shrink partition D (or E), they find that they still cannot extend the C drive in Windows Server 2016.
This occurs due to the following structural reasons:
- The Extend Volume function can only add unallocated space to the contiguous partition located immediately on its left side.
- The Shrink Volume function can only generate unallocated space on the right side of the shrunk partition.
As shown in the screenshot, after shrinking the D: drive, 20 GB of unallocated space is created on the right side of D. Because this space is non-adjacent to the C drive and sits to the left of E, the Extend Volume option is disabled for both partitions.
This is the most common reason why administrators cannot extend volumes in Windows Server 2016 Disk Management. To resolve this issue, you must move the unallocated space so that it sits directly behind the C drive.
Steps to resolve when you cannot extend a volume in Windows Server 2016 after shrinking:
- Download NIUBI Partition Editor, right-click drive D:, and select "Resize/Move Volume". In the pop-up window, drag the middle of the partition toward the right. This moves the unallocated space directly adjacent to the C: drive.
- Right-click the C: drive, select "Resize/Move Volume" again, and drag the right border toward the right to merge the unallocated space.
- Click Apply on the top left to execute the changes.
NIUBI Partition Editor is designed to operate in Virtual Mode; your actual disk partitions will not be altered until you click Apply to confirm. If you make a mistake, simply click "Undo" to cancel. Pending operations marked with 
can be completed directly within Windows without rebooting the server.
Watch the video how to operate:
2. Why You Cannot Extend Partition in Windows Server 2016 After Deleting
Since Disk Management cannot extend partition C after shrinking D, some administrators try deleting the D drive instead. However, they find that the Extend Volume option remains disabled. There are two common reasons why you might be unable to extend a volume in Windows Server 2016 via Disk Management even after deleting the adjacent partition.
① The Extend Volume function natively supports extending NTFS, ReFS, and RAW (unformatted) partitions. FAT32 and other unsupported partition types cannot be extended, even if there is contiguous unallocated space on the right side.
② The partitions being deleted and extended use mismatched types. On an MBR disk, the free space created by deleting a Logical Drive cannot be extended into a Primary Partition. Similarly, unallocated space outside an Extended Partition cannot be merged into Logical Drives.
If you are unable to extend a volume in Windows Server 2016 due to an unsupported FAT32 partition or type mismatches between primary and logical partitions, you can easily resize the partition by dragging and dropping with NIUBI Partition Editor. Follow the steps demonstrated in the video tutorial:
3. Why You Cannot Extend Volume Past 2TB in Windows Server 2016
For enterprise servers, it is very common to deploy large 2 TB to 4 TB standalone disks or RAID arrays exceeding 10 TB. However, if a disk is initialized using the legacy MBR partition style, a maximum of 2 TB of space can be addressed. The remaining space will appear as unallocated and cannot be used to create new volumes or extend existing partitions.
As shown in the screenshot, even though drive H is formatted as NTFS and has contiguous unallocated space on its right side, Disk Management is still unable to extend this partition due to MBR limitations.
If you cannot extend a partition past 2 TB in Windows Server 2016, you must first convert the disk from MBR to GPT. Once converted, you can easily extend the partition into the unallocated space. Watch the video tutorial below to see how this is done:
In Summary
If you cannot extend a volume in Windows Server 2016 using Disk Management, determine the cause based on your specific disk partition layout and apply the corresponding solution outlined above. Beyond shrinking, moving, and extending partitions, NIUBI Partition Editor helps you merge, copy, convert, defragment, wipe, or hide partitions, scan for bad sectors, and perform many other tasks. It operates significantly faster than alternative tools due to its advanced file-moving algorithm. Most importantly, it features unique 1-Second Rollback, Virtual Mode, Cancel-at-will, and Hot-Clone technologies to completely safeguard your system configuration and data integrity.
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