I finally got serious about starting to configure back-ups for all users, and after setting up only a few with largely default options and "simple schedules" I've run into a problem that I just knew intuitively was going to be an issue with using just "simple schedules" for all domains. Back-ups have started failing with this error:
Waiting for the number of running backups to drop below the system limit of 3 ..
.. gave up waiting after 120 seconds
What is the acceptable, logical and scalable way forward here? It never did make sense to me that all domains on the server would run back-ups at midnight (along with all of the other cron jobs that run at midnight), but manually keeping track of hundreds of domains running back-ups a few minutes apart is going to be a nightmare of monumental proportions, exactly the kind of manual busy work that control panels like Virtualmin are supposed to eliminate.
I'd appreciate your thoughts on this.