Virtualbox: Shrinking VM Disk Images

Source: http://snippets.khromov.se/shrinking-a-virtualbox-linux-image-with-zerofree/

• Download the SystemRescueCd Live Image
Mount it as a CD on your virtual machine and boot into the live distro
• Find all available partition and LVM (volume groups) with:

fdisk -l

• After we find our partition run zerofree to zero out the free space. In our example we will run it on the LVM root partition

zerofree -v /dev/mapper/vg_rheldev-lv_root

• Finally, boot down your virtual machine, and run VBoxManage on the host to resize the .vdi file

C:\>"c:\Program Files\Oracle\VirtualBox\VBoxManage.exe" modifyhd "c:
\Users\jerome\VirtualBox VMs\Monster\Mobiquithings.vdi" --compact

With this method, my VM shrunk from 200 GiB to 26 GiB

NB: The other method mentioned on the net replacing zerofree with dd like in

dd -if /dev/zero -of /bigemptyfile -bs 4096; rm /bigemptyfile

was not satisfactory for me.