PS C:>(Get-Virtual).info

I get many requests to extend the C:\ (or any other drive)
Most times these are for VMs – so it is pretty easy right? Extend the amount of disk allocated to the virtual machine, then extend in Computer Management – or using diskpart?

Well this does not always work – see, Windows does not really like you messing with system drive.

Well, Dell have come up with a brilliant tool called EXTPart
http://support.dell.com/support/downloads/download.aspx?c=us&cs=19&l=en&s=dhs&releaseid=R64398&formatcnt=2&fileid=83929

All you need to do now is provision the extra space to the VM, then run the tool at the command line and follow the wizard:

C:\>extpart.exe
ExtPart - Utility to extend basic disks (Build 1.0.4)
(c) Dell Computer Corporation 2003

Volume to extend (drive letter or mount point): c:
Current volume size : 66285 MB (69504860160 bytes)
Current partition size : 76285 MB (79990815744 bytes)
Size to expand the volume (MB): 76285

that’s it – job done . . zero downtime (watch out of course . . this works differently if you have a clustered disk to extend – see:  http://www.get-virtual.info/2011/01/25/replacing-clustered-storage-for-a-sql-cluster-emc-ce-ms-clustering/ )