VirtualBox

How to compact the virtual disk image

[1]

1. Defragment hard drive (in guest system)
   e.g. using Defraggler
2. Write zeros to hard drive blocks of free space (in guest system)
   e.g. using nullfule
3. Compact the VDI virtual disk image (in host system)
   by running

VBoxManage modifyvdi image.vdi compact