Need to extend a disk on a server using XenXenter. This is for using the XenCenter GUI and Windows Vista/2008
1. Shut down the VM in XenCenter
2. If you want, make copy of VM in XenCenter
3. In XenCenter GUI, set the new size of the system disk for the virtual machine (i.e. grow from 20GB to 30GB) along as you have the space free on the volume. So select VM, and choose Storage and select properties
4. Change the DVD drive of the virtual machine to boot off the Windows Vista or 2008 DVD iso image as this will allow the use of diskpart.
5. Click Next and then choose Repair your Computer.
6. Click Next and then choose Run Command Prompt and type diskpart.
7. Run the below commands
type list disk
type select disk <number
type list volume
type select Volume <number
type extend , when no parameter specified all the space will be used to extend
type exit from the Diskpart utility and type exit fromm command prompt. Select reboot from menu
8. Your system disk will now be extended.
Citrix wrote this article which describes many of these steps: How to grow size of XenServer Windows 2003 System Disk VM http://supp