Virtualbox 壓縮 vdi

待測
VBoxManage modifyvdi winxp.vdi compact

the following three steps will compact your VDI file:

1. Defragment hard drive (in guest system)
2. Write zeros to hard drive blocks of free space (in guest system)
3. Compact the VDI virtual disk image (in host system)

http://my.opera.com/locksley90/blog/2008/06/01/how-to-compact-a-virtualbox-virtual-disk-image-vdi