I have recently saved a lot of disk space by overwriting unused (empty) disk space within a VM with 0s (zeros) and then recloning the VM.  When all your empty disk space is 0’s, there’s a huge compression benefit.  Here’s how it played out, and how I saved 10 GB of raw disk space.

  • I started with a VMware machine that consumed 30 GB of space on my host hard disk
  • The VMware machine had a 35 Gb hard disk, of which 16 Gb was free space
  • I downloaded “sDelete” from Microsoft (formerly a Sysinternals tool)
  • I defragmented the drive, using the Windows XP defrag utility (I don’t think this had any impact other than speed optimization)
  • Installed sDelete in the VM, and from the command line ran “sDelete -c”.  This overwrites all empty disk space with zeros
  • I then cloned the VM (full independent clone)
  • The result was that the VMware machine now consumed only 20 GB of space on my host hard disk.

Bottom line – this processed saved me 10Gb of hard disk space.  Hope you get similar results.