How To Shrink Your Virtualbox VM And Free Up Space For Your Hard Disk. Knocked 30Gb off my work virtual machine. Something I think I'll start scheduling to do every 6 months or so... The issue is that dynamic disks under VirtualBox only grow, they never shrink. So every time you save a file to your VM the disk grows, even if you delete it immediately. Running SDelete and then cloning (and then just using the clone) will free up that space since the cloning process doesn't copy empty disk space.