The worst time to learn how your backups work is right after a griefing. Here's the setup we recommend for every server.
Apply the 3-2-1 rule
Keep three copies of your world, on two kinds of storage, with one off-site. Campfire handles the automatic snapshots and off-site copy; you just add a manual backup before big updates.
Always take a manual backup before installing or updating a mod. It costs ten seconds and saves entire weekends.