How to resize a VirtualBox vmdk file

source https://stackoverflow.com/questions/11659005/how-to-resize-a-virtualbox-vmdk-file 

Resizing with the command

vboxmanage modifyhd Machine-disk1.vmdk --resize 30720

gives the error

Progress state: VBOX_E_NOT_SUPPORTED
VBoxManage: error: Resize hard disk operation for this format is not implemented yet!

you have to do

VBoxManage clonehd "source.vmdk" "cloned.vdi" --format vdi
VBoxManage modifyhd "cloned.vdi" --resize 51200
VBoxManage clonehd "cloned.vdi" "resized.vmdk" --format vmdk