I believe that there are qcow2 files that displace a small amount of gigabytes on a server (as verified with a df -h on the physical server) yet allow for lots of space when you log into the virt-manager VM and issue a df -h. How do you create such a file? How does the physical server know that there won't be a problem if/when the VMs grow to their maximum size and potentially fill up the physical server?
The truncate command doesn't create small qcow2 files. Virtual Machine Manager's GUI allows the creation of "hardware" via the GUI. Both of these methods of creating .qcow2 files create files that are the maximum size.