I've recently made a "backup PC". It's basically a spare PC that is only used if my main PC suffers a major problem. It has a copy of my Steam folder which is about half a terabyte. What I really want to do is keep that folder an exact copy of my main PC's folder. Now in the past, being a backup simpleton, I would just copy folders to back them up, but with a folder that big it takes several hours. What I need is, when the backup PC is on, it checks to see what files need updating and updates them. Or I could instigate a sync from my main PC. Either solution will do. The main thing is that I need something that will only update the files that have changed and the update should be one way only. main PC to backup PC. But I am not well versed in backup software. Can folks suggest some software to do this?