VirtualBox can export virtual machine images which is handy if you want to give someone a ready to use OS for example.
I had an old scanner which I was driving under XP, using the USB forwarding feature. I wanted to give a friend the scanner and an OVA image containing the ready to go OS. The problem is that unused blocks on the NTFS filesystem will affect the compression of the image. Even though I had defragmented the virtual disk and moved the used blocks to the front using a pre-8.0 version of Ultradefrag, the unused blocks after the used area still contained old random data.
Enter sdelete. This is a free utility from Microsoft that wll zero unused blocks. You use it like this:
sdelete -z c:I ran this once on the virtual disk, then shutdown the virtual machine and exported it to OVA format. The result was quite satisfactory; what was once a 5.1 GB dump turned out more like 2.1 GB.
