After some time qcow2 images tend -especially after taking snapshots- to grow bigger and bigger, even bigger than the maximum size specified at creation time. QEMU provides a tool called virt-sparsify (install libguestfs-tools package in CentOS 7) that can effectively make a virtual machine disk thin provisioned (space is not preallocated, only the actual space needed is used). virt-sparsify has a nice number of options, the most interesting one is --in-place, it tells QEMU to shrink the volume in place without requiring any addition space. …