There're main 3 reason that diskpart in command prompt would fail to extend the volume and showing this error message: The Volume You Have Selected May not be Extended, please select another volume and try again
Error message screen shot
We still have 2 methods to extend C Drive after understanding the limitations of diskpart, the two plans are:
Well, actually we can extend c drive with diskpart command line only when the file system is NTFS and there's unallocated space followed to it, and what's the most important is, before Windows is running, yes, we can enlarge system partition size in the command prompt tool before we entering to the operating system, so we need to press F2 or other access keys according to the hint from the start screen like the info below:
Then we choose command prompt and type diskpart
to use this tool like this
Command are:
Although we can do it successfully within diskpart, not everyone has the same conditions, which are, NTFS file system on C Drive and enough unallocated space available at the right place, so if we don't satisfy our disk on our Server system or client system, we can turn to the second method
When diskpart fails to extend the volume because of the file system and the unallocated space problem, we can use Partition Expert to do the same job without any limitations, this software, by the way, is also a portable program and has separated 32-bit and 64-bit packages, so you can either install it or directly run it from the portable package, OK, let's extend system volume within the following steps:
Then you'll have a larger C Drive without warring about the low disk space alert and not enough disk space problem on this partition any more, of course, when some day it becomes less in free space, run the software again and resize it with more free space is still an easy job.