That's not differential backups, that's optimizing the mirroring algorithm. Differential backup here means that if a file has changed you only send the change

That's not differential backups, that's optimizing the mirroring algorithm. Differential backup here means that if a file has changed you only send the change delta, not the whole file. This is what makes it possible tobrun that kind of things every hour if needed even on large folders. If s3 supported that and with the already existing versioning you'd have a pretty kickass solution; that's basically what you can do with rsync and a zfs filesystem for example