Primary Partition is always the partition with system boot data in it, because system can only be installed on primary partition. Add unallocated space to this partition need some steps depends on what system you’re using.
Windows Server 2003, partition resizing on this system requires unallocated space continuous to primary partition so that you can Extend Volume on C Drive to extend.
Windows Server 2008, Windows Server 2012, Extend Volume will not gray out if you have RAID 5 array in Server, each disk can set up at most 4 primary partitions, and adding unallocated space to RAID 5 primary partition is easier.
Click on any partition to extend primary partition, if unallocated space available on any disk, if every disk has unallocated space, and the primary partition you extend is not next to it. Server system will warning you to convert dynamic disk if insist so. Dynamic disk will not allow system boot on any partition of the disk, you it’s a better way to manage disk space and server performance if you have many data partitions on different disk.
Window 7, Window 8, and Window 10, on the other hand, if the unallocated space is not next to primary partition, Extend Volume will gray out, and it’s impossible for disk management to move unallocated space from one partition to another, or from the end of disk to the top of it.
What causes you ask this question might be the warning of low disk space on Server primary partition. It’s not strange and it’s not necessary to get confuse on it when you seeing large amount of free space on other partitions available. Server system will not distribute disk space automatically when some partition gets low disk space warning. It’s a pre-setting program on disk space. Even if you already have made enough space on the primary partition at the beginning, system will run on low disk space after long time using. What necessary is to find partition magic server to manage disk space in everyday use.
Partition Extender, the partition software to add unallocated space to primary partition under the following situation you might meet or about to meet in the future. Disk Management will do the extension when the disk map is C Drive + Unallocated space, or primary partition + unallocated space. See more below:
Primary partition + Unallocated space
Primary partition + Unallocated space + D partition
Primary partition + D partition
Primary partition + D partition+ Unallocated space
Primary partition + D partition+ Unallocated space + E partition
Primary partition + D partition+ Unallocated space1 +E partition +Unallocated space 2