The qcow2 format is preferred over "raw" because it supports snapshots and occupies less space on the host by only using what is actually written to the disk. : Use the qemu-img tool to create the initial file. qemu-img create -f qcow2 windows7.qcow2 40G
The file only takes up the space actually used by the OS. windows 7 qcow2 top
: You can create a "top" or overlay image that uses a read-only base Windows 7 image as its backing file. This allows you to create multiple "clones" that only store changes (writes) in a small overlay file, saving massive amounts of disk space. The qcow2 format is preferred over "raw" because
To create a properly sized qcow2 with advanced features: windows 7 qcow2 top