My WinXP VM ran out of space on its drive C, and after looking at many posts (lots of people have the same problem) and finding only partial answers I worked it out and here is the definitive procedure. Please feel free to advise and correct, but this really ought to be in the Parallels help.
This procedure applies only to Virtual Hard Disks (not to Boot Camp disk partitions), and requires temporary disk space equal to the sum of the existing drive plus the new expanded drive. The reason for this rigamarole is that Windows cannot alter the partition size of its boot disk. So we have to create a temporary copy of the boot disk, boot from it, and then we can modify the partition size of the expanded drive. Then we throw away the temporary hdd.
In the Finder, click on the existing drive image, probably "Winxp.hdd"
File > Duplicate (cmd-d)
MacOS makes a duplicate of your drive image, "Winxp copy.hdd"
Start the Parallels Image Tool
Select the old drive "Winxp.hdd"
Set the desired new size
Let the Image Tool do its thing (takes a while)
Start Parallels and edit the configuration of the VM
click on Hard Disk 1
click Remove (removes "Winxp.hdd" from the config)
click Add; select Hard Disk; click Next; click "Use an existing..."
Browse to find the copy drive, "Winxp copy.hdd"
(The copy drive image is now Hard Disk 1.)
click Add; select Hard Disk; click Next; click "Use an existing..."
browse to the expanded drive "Winxp.hdd"
(The expanded drive is now Hard Disk 2.)
Boot the VM. Wait for Windows to get completely up and stable.
Click Start; click Run; type: diskpart (return)
In the diskpart.exe window type: list volume (return)
You should see two disk volumes, C and E.
type: select volume 2 (return)
type: extend (return)
After a moment you see: DiskPart successfully extended the volume.
type: list volume (return)
and observe that volume E now has the expanded size.
Click the red STOP button in the upper right (no need for shutdown)
Edit> Virtual Machine
Click on Hard Disk 1, "Winxp copy.hdd"
Click Remove
Click on Hard Disk 2, "Winxp.hdd"
Click Remove
Click Add; select Hard Disk; click Next; click "Use an existing..."
Browse to the expanded "Winxp.hdd"
The expanded "Winxp.hdd" is now Hard Disk 1
Click OK
Boot the VM.
Windows will discover new hardware.
Windows will notify you of a System Settings Change and ask if you want to restart now?
Click Yes.
Windows reboots.
This time Windows will be normal and drive C has the expanded size!
You can now go to the Finder and delete "Winxp copy.hdd" and empty the trash.
P.S. at the end you might think, after Removing HD#1, "Winxp.hdd" is now HD#1, I'll just go ahead and boot. Nunh-unh! I tried that and Parallels then said, there's no bootable system on that disk. Aghhh! But if you follow the instructions, delete both drives and then add back the expanded one, all will be well.
Last edited: Oct 20, 2008