rsnapshot is a backup utility that uses rsync to backup files over the network. Backups to my external Btrfs drive were dragging, with a lot of time and processor power spend running cp and rm. With a COW filesystem like btrfs, this is wasted processor time and disk activity, so I migrated to using Btrfs snapshots instead. Walter Werther has a good write up. The idea is to configure rsnapshot to use scripts that wrap btrfs instead of your system's cp and rm programs. Walter's put the relavant script on GitHub: cp and rm.