Sparse files are nice to use to store virtual machine’s virtual disks but can be a real pain in the ass to backup efficiently, especially over the network. Luckily rsync provides a way to intelligently copy sparse files both locally and over the network. The trick is use --sparse and --inplace options. Let’s say we have a sparse 60 GB qemu virtual disk with only around 7 GB used: $ ls -lh fedora24.qcow2 -rw------- 1 root root 61G Nov 8 19:11 fedora24.qcow2 $ du -h fedora24.qcow2 7.2G fedora24.qcow2 The first thing to note is that ls does not recognize sparse files while du does. The first time a file is copied use the --sparse option: …

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. …