This technical article outlines the steps required for extending the C: drive of a Windows Server 2003 R2 virtual machine running under Windows Server 2012 R2 Hyper-V.  Please note you can also use this identical technique for expanding Windows 7 and Windows 10 virtual machines running under Windows Server 2012 R2 Hyper-V and later. 

However, this technique is only applicable for expanding the C: drive, if it contains the OS and registry, and only if there is no D (or subsequent) drive space allocated following the C: drive. 

• a server running Windows 2012 R2 Hyper-V role (or later such as Windows Server 2016 or Windows Server 2019 (recommended))
• DISKPART.exe utility program, included in Windows Server 2012 R2

• A virtual hard disk (a .vhd or .vhdx file) is running out of space or has grown to a point where there isn't enough space to install new programs, perform Windows Updates or write database records


• You want to learn about new capabilities that are gained through the use of virtualization techniques.  For example:


• by using this technique to expand the size of the C: drive, concerns for running out of space are reduced.  Therefore it is no longer necessary to consider allocating a maximum potential size (when setting the initial size of a new virtual machine C: drive).


• you can toggle between fixed and dynamic sized disks (by changing settings (for the most part)).  Thus, it is easier to research whether fixed sized disks result in significantly better performance in your configuration (and are worth the additional overhead involved in storing and backing up (copying) the larger .vhd and .vhdx file sizes).  However, the steps to do this are no longer covered in this technical article due to the differences in Hyper-V 2012 R2 (although easier) as opposed to Microsoft Virtual Server 2005, which is now obsolete.

We are going to run the utility programs on a physical host machine running Windows Server 2012 R2 Standard x64 Edition SP2 (or later) in a Hyper-V role.

The guest OS installed on the .vhdx used in this example is Windows Server 2003 R2 Standard Edition SP2 (x86).  But this works for nearly all guest OS including Windows XP, Windows 10 x64 and Windows 2012 R2 x64 all the way up to Windows Server 2019.

This technique is known to work using .vhd and .vhdx images holding machines running Windows 2003 R2 OS and later.  If you are running Windows Server 2012 R2 in the virtual machine, it will not be necessary to run the DISKPART utility from the command line in the physical host, you can do all you need to do to accomplish the expansion by changing the settings alone.

• In most cases it will make sense to create a new backup copy before going live and into production mode.
  
  Start up the virtual machine.
  You have succeeded!