Have you ever encountered such a problem that you
cannotmerge unallocated space to C: drive? Imaging you has a Windows
Server 2008 R2 Enterprise whose Disk capacity is 116GB. It is divided into C: drive and
D: partition. The former contains system and boot files while the latter includes data
of user. Now you want to extend C: drive due to its running out of space. There happen
to be a large amount of free space in D: partition. You can shrink D partition to
generate 30GB unallocated space with the help of the built-in disk management. What a
pity, you will find the “Extend Volume” grayed out when you are
right-clicking C: drive. So, how can we merge unallocated space to C: drive on earth?

In fact, the "Extend Volume" function is
available only the unallocated space is contiguously on the right side of the
partition which you would like to extend. That’s why you fail to "Extend Volume".
In order to solve this problem, here come two
solutions:
Solution 1:Merge unallocated space to C drive with
AOMEI Partition Assistant.
Partition Assistant is professional, which enables you to merge
unallocated space without losing any data. It also allows you to resize, move and
create partition, etc.
As for step-by-step instructions illustrated on how to merge unallocated
space to C drive, please check the reference here.
Merging unallocated space to C drive with Partition Assistant software
can be really very easy. There are Pro
Edition, Server Edition, Unlimited
Edition and Technician Edition available for different
operating systems. You can free download Partition Assistant demo version to have a
try before you buy full edition.
Solution 2: Merge unallocated space to C drive withDisk Management snap-in after backing up D partition and deleting
it.
Step 1: Make data and files of D partition backup.
Step 2: Open Disk Management by Right-clicking "Computer"
-> "Manage" -> "Storage" successively.

Step 3: Right-click on D partition and select "Delete
Volume".
Step 4: Then, a block of unallocated space behind C
drive appears. Select "Extend Volume" after Right-clicking C drive. Merge
unallocated space to C drive with the help of the "Extend Volume Wizard".

Comparing two methods, Partition Assistant is more convenient with high
safety. So, merging unallocated space to C drive by using AOMEI Partition Assistant
can be a good choice.