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
ALARA Conseil 