Auto Saves/Backups

Factorio has a built-in "backup" system called auto save slots, where every time the server saves it creates a copy of the world instead of saving to the original world file. This acts as a standard backup system, but instead of backing up the save indirectly, it does so every time the world is written to the disk.
The original save file is written to under similar conditions to when you're playing single player, like when all players leave the server or when the server restarts. So under normal play, your world is saved to the auto save slots, and then saved to the main save slot when the server pauses or stops, just like in single player.

Configuring

You can configure the auto save frequency and the amount of auto saves kept using your server's Startup Parameters, specifically the Auto Save Interval and Auto Save Slots parameters.

The Auto Save Interval starts when the server is resumed, like when a player joins the server, and resets when it's paused.

The Auto Save Slots are used by generating an _autosave[#].zip file in your saves folder, which contains the contents of the [saveName].zip file.

Restoring

You can easily restore to a Factorio autosave using the WinterNode game panel by renaming the _autosave[#].zip file to the name of your [saveName].zip file.

make backups!

Make backups/copies of the files you're changing! That will save you if you make a mistake!

1. Stop your server.
2. Navigate to the saves folder using the File Manager
3. Make a copy of the [saveName].zip file.
   Delete the original
4. Make a copy of the _autosave[#].zip file you want to restore to.
   Look at the timestamps on the far right of the file table for when the auto saves took place.
5. Rename either the copy or the original _autosave[#].zip to the name of your [saveName].zip
   For example, the default save name is gamesave so the file name would be gamesave.zip.