Zero-Out Storage

Unfortunately, VirtualBox does not automatically zero-out free space of Windows virtual machines. This requires a manual process in order to reclaim space.

From within the Windows VM, first clean-up space and empty the recycle bin. Then, zero-out all free space by running the following command as administrator:

sdelete -z C:

Then, from the host, reclaim all free space from the virtual machine VDI hard disk file:

VBoxManage modifyhd [disk.vdi] --compact