SHELL

rsync only new files

rsync -r source_folder/ target_folder/ --ignore-existing 

rsync only updated files

rsync -r source_folder/ target_folder/ --update

rsync keep old files

rsync -vzrb --backup-dir=_old_ --suffix=$(date+_%F-%T) --update --times /path/to/source backupuser@1.2.3.4:./path/to/destination