If you follow the example in my Summit handout you can use virt-df to monitor your VMs’ disk usage over time. But what if your VMs migrate between hosts or get renamed? Previously you had to rely on the guest name being unique and not changing. In libguestfs 1.12 we have changed most of the virt tools so you can now use a UUID to specify guests instead of a name.
# virt-df -d 799ae7ca-23a2-f622-c691-48feebcddbe6 -h Filesystem Size Used Available Use% 799ae7ca-23a2-f622-c691-48feebcddbe6:/dev/sda1 484M 67M 393M 14% 799ae7ca-23a2-f622-c691-48feebcddbe6:/dev/vg_f13x64/lv_root 7.4G 4.3G 3.1G 58%