Suppose that you have more than one server, and that you want to keep a backup of your unRaid server.  Suppose that you have tried the sync options, but find that they are a bit finicky and unreliable.  This is a totally reliable bullet proof / stable way to keep your backup server fresh.  All you need is 2 unRaid servers connected to the internet, and we use secure keyed ssh to make the rsync commands secure and optimized for transiting the internet.   What I am using is a unRaid 6.2.