assuming 2nd folder is a mounted drive on another server.


app2 /backup folder is actually app1's backup folder



allow server dir to be access by another server - https://serverfault.com/questions/410588/how-to-mount-a-directory-from-another-server 


-- NFS SERVER


On the 'server' add an entry into your /etc/exports to share the directory e.g.

/directory/with/data secondserver.tld(rw)

which allows secondserver read/write access to the directory/with/data

then use exportfs to share the directory

exportfs -r

Add to etc/hosts.allow the IP or ALL: LOCAL of the client server


--- CLIENT


mount volume on other server - 

add to fstab 

example is -    74.50.55.68:/backup-tomdata /backup-tomdata    nfs rw 0 0 

rern fstab mounts - 

mount -a



https://www.marksanborn.net/howto/use-rsync-for-daily-weekly-and-full-monthly-backups/#:~:text=Rsync%20is%20a%20sweet%20utility,slow)%20method%20using%20md5%20hashes.




RDIF


https://rdiff-backup.net/docs/examples.html#backup