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To reduce the size of virtual disk images
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About Virtual Disk Compact and Copy

To reduce the size of virtual disk images

What is CompactVD?

CompactVD is a utility to optimize the size of dynamic disk images, based on the bitmap allocation tables of known file systems. You can check if there is wasted space in a dynamic disk image comparing the size of the disk image file with the space used by file systems inside the image. For a optimal resource allocation, they should not be very different.

Currently supported file systems are:

  • Windows: New Technology File System (NTFS)
  • macOS: Hierarchical File System (HFS)
  • Linux: Extended File System (EXT)

Compact Disk Image In Place

The compact operation pulls blocks of data from the end of the disk image to space that was detected to be not in use by file systems.

To begin a scan is made to detect blocks of data that are not in use by file systems, and the disk image structure is updated marking those blocks as if they were never used. Then blocks with effective data are moved from the end of the disk image to the space that was recovered by the previous operation.

Finally the image structure is updated to reflect the new position of the moved blocks, and the image file size is trimmed. Updates to the image structure are temporarily saved on the host media and will be written to the image at next program execution, in case of a recoverable hardware failure.

Copy to New Disk Image

The copy operation begins with a scan to detect blocks of data that are not in use by file systems. The new image is created ignoring those blocks, and blocks that would otherwise be completely filled with zeros.

The format of the new disk image can be select in the Copy Disk Image dialog with one these file extensions:

  • VDI, Virtual Disk Image for Oracle VirtualBox
  • VMDK, Virtual Machine Disk for VMware products
  • VHD, Virtual Hard Disk for Microsoft products
  • RAW or ISO, for a complete disk image

Copyright Notices

Licensed under the Apache License, Version 2.0.

The application icon is a derivative work of original made by Susumu Yoshida (Copyright © 2009 McDo

The other icons that identify image disks in the view panel are copyright-protected computer icons of file formats. The author believes that the exhibition of icons to identify the file formats in question qualifies as fair use.

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