I am having a problem making a key of ssh using rsync

[chris allen]

I have a main server that I want to backup to my backup server.  I don't 
know on witch side that I need to make a key on

the code is bellow is what I am using

rsync -e "ssh -i /root/.ssh/rsync-key" -avHRrz --numeric-ids   
--progress   --stats  --delete --exclude=/proc/* --exclude=/tmp/* 
--exclude=/lost+found/*  / backup at mcncyo.homeip.net:/home/backup/luke

mcncyo.homeip.net is the backup server

mychristiannetwork.com is the main server

Can someone tell me on what side needs what to make this work.

rsync works fine except  it keeps asking for a password.