Symptoms

On attempting to compress the virtual hard drive Parallels Desktop displays the following error:

    Hard disk %1 used by the virtual machine \"%2\" cannot be compressed
    The disk is either plain, or dynamic, or contains no data. Such disks cannot be compressed

Cause

Parallels Desktop cannot compress the following types of the virtual hard disk:

• Dynamic Disk
• Disk with GPT partition scheme
• Disk with empty MBR (master boot record)
• Disk with snapshots
• Rollback mode
• Plain Disk

Resolution

• Dynamic Disk - compressing is not supported in the current version of Parallels Desktop
• GPT Disks - compressing is not supported in the current version of Parallels Desktop
• Disk with empty MBR - compressing is not supported in the current version of Parallels Desktop
• Disk with Snapshots - merge all snapshots and try compressing again

To merge snapshots, please do the following:

1. Right click your virtual machine in Parallels Desktop Control Center and choose Manage Snapshots.

   

2. Choose snapshots one-by-one starting from the left side and click Delete.

   

Alternative way:

Follow step-by-step instructions from the article below (Advanced Troubleshooting):

http://kb.parallels.com/9165

• Rollback mode - disable rollback mode feature by going to configuration > Security > Rollback mode > Disable.

• Plain Disk - convert disk type to Expanding by going to configuration > Hardware > Hard Disk # > Edit... > check Expanding disk checkbox > Apply.