Virtual Hard Disk File Size Is Greater Than the Used Disk Space That Is Reported by the Windows Guest Operating System (824517)

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When you install a Windows operating system on a guest PC that you create, Setup copies a number of temporary files to the hard disk of that guest PC. These temporary files are typically removed when the operating system installation is complete. However, the guest PC virtual hard disk image expands to hold the temporary files. When the temporary files are removed, the virtual hard disk image does not automatically contract. To resolve this issue, compact the virtual hard disk image.

Note To complete the following procedure, you must obtain a third-party utility to remove ("zero out") data from the hard disk of the guest operating system. For additional information about one of these third-party products, visit the following Tolvanen Web site:Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.

1. Start the guest PC, and then defragment the guest PC hard disk.
2. Obtain and then install a third-party data removal utility on the guest PC operating system.
3. Run the third-party utility in the guest PC, and then configure it to zero out unused disk space.
4. When this operation is complete, shut down the guest PC.
   
   If you use "undoable" virtual hard disk images, commit the changes to the virtual hard disks.
5. In Virtual PC, click Virtual Disk Wizard on the File menu.
6. Click Next, click Examine or modify existing disk image, and then click Next.
7. Click Browse, locate and then click the virtual hard disk image that you want to compact, click Open, and then click Next.
8. Click Compact the disk image, and then click Next.
9. Use one of the following methods to create a compacted disk image:
   • Click Use original file.
     
     When you use this method, the virtual hard disk image is compacted to the same file as the original virtual hard disk image. This method uses less disk space on the host computer. However, if the virtual hard disk file becomes corrupted during the compaction process, you may lose guest PC data.
   • Click Select new file, click Browse, type a new file name for this virtual hard disk image, and then click Save.
     
     When you use this method, a new image file is created for the compacted virtual hard disk image. Because the original file is not overwritten during the compaction process, Microsoft recommends that you use this method. When you use this method, you can verify the integrity of the guest PC virtual hard disk before you have to remove the original virtual hard disk image.
10. Click Next, and then click Finish.
    
    The virtual hard disk is compacted.
11. On the message that states that the hard disk was compacted successfully, click Close.

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.