Increasing the size of disk is shown on VirtualBox platform.
Increasing the size of disk on other hypervisors, like VMWare ESXi and other, is different, because it have another functional.
Virtualbox platform was installed on Ubuntu 16.04.
Look at our disk in system.
Go to directory in Ubuntu, where is image of virtual machine.
Look information of this image with VirtualBox built-in program.
Check image again.
Start server and booi in Single User Mode.
Look at our disk.
Size is changed, but we have CORRUPT status.
Growup file system.
Check disk with df.