Symptoms

Parallels Desktop displays the following error message when you are trying to compress virtual machine's hard disk:

    “The disk cannot be compressed because it is used by the "*VM-name*" virtual machine that is in Safe mode or Undo Disks mode, or has snapshots”

Cause

• Virtual machine's hard disk has snapshots
• Rollback mode option is enabled
• Virtual machine hard disk is corrupted
• Virtual machine hard disk has hidden partitions or unallocated space
• Virtual Machine was imported from Boot Camp

Resolution

Try to compress virtual hard disk after every single resolution step you take:

1. Make sure the virtual hard disk does not have Snapshots:

   • Make sure there are no snapshots. Go to Actions -> Manage Snapshots.. and delete all snapshots.

   If there is an error deleting snapshots or there are no snapshots listed, proceed to Advanced Troubleshooting part of this article.

2. If your virtual machine was migrated from a real PC, make sure it does not have unallocated space. You may check it in Windows Start menu > Control Panel > Administrative Tool > Disk Managment.

Advanced Troubleshooting

1. In Mac OS X, go to Applications > Utilities and launch Terminal.

2. Paste the command below into Terminal as is (do not hit Enter yet):

   prl_disk_tool merge --hdd
   

3. Find your virtual machine in Finder. Right click on the .pvm file of your virtual machine and choose Show Package Contents.

4. Drag your WindowsXXX.hdd file into Terminal and drop it inside the window. In Terminal you will see a similar outcome:

   prl_disk_tool merge --hdd /Users/Username/Documents/Parallels/Windows\ 7.pvm/Windows\ 7-0.hdd
   

   Please note there should be a space between --hdd and /Users/Username...

5. Press Enter key to start merging Snapshots. Once this is done, try to compress virtual hard disk again.