I am using lftp and mirror. One server functions as the “main” server, which mirrors the backup server to itself once per day at a specific time (they both run 24/7 so I set it to run very early in the morning when it is unlikely to be accessed).
In my crontab I have:
# * * * /usr/bin/lftp -e "mirror -eRv [folder path on main server] [folder path on backup server]; quit;" sftp://[user]@[address of backup server]:[port number]
No problem! Glad I could be of help, and best of luck on your project.