This question arose from “Is it safe to answer “erase disk and install Ubuntu” on a virtual machine?”.
Guest space from host:
What happens when the disk space gets larger than the unused disk space, perhaps not at start, but later, when the usage grows e.g. to 40 out of 50 GB and your main drive has only 40 GB space left? In other words, will the VM ever overwrite data, or will it report this? I do not think that the VM will ever overwrite data of the host, I just want to be sure.
Host space from guest:
And the other way round, what if the host disk wants to use space that is guaranteed to the guest, is there a chance that it can damage the guest somehow, and is it possible at all? Will the host just tell you that host space is limited due to that VM?
Guest space to guest:
Just an example from Oracle VirtualBox — or any similar VM software — installing Linux Mint guest on Windows 10 host, using “thin provisioning.” The installer tells me directly after the choice of the “Erase” option:
“If you continue, the changes listed below will be written to the disks. Otherwise, you will be able to make further changes manually. The partition tables of the following devices are changed: SCSI3 (0,0,0)(sda) The following partitions are going to be formatted: partition #1 of SCSI3 (0,0,0)(sda) as ext4.”
I have chosen “Continue” and nothing bad has happened. Probably, the message pops up because I have another VM already installed. It seems as if the VM can take space from another VM, is this possible?
This question is not restricted to the usage of Oracle VirtualBox; this question is meant as a general question about VMS in general, not excluding answers on VirtualBox of course.