Compacting a VirtualBox VDI image
Firstly, you’ll need to install
zerofree on your Linux image, then mount the root partition as a read only volume. This can be done via:
sudo apt-get install zerofree sudo apt-get clean sudo reboot # interrupt grub boot and boot into recovery mode mount -n -o remount,ro -t ext4 /dev/sda1 / zerofree /dev/sda1 shutdown -h now
And now on the Windows Host:
"C:\Program Files\Oracle\VirtualBox\VBoxManage.exe" modifyvdi "VirtualBox VMs\server\server.vdi" compact
This should make the VirtualBox image more in line with the calculated size it should be.