Backing up RHEL5 and 6

Hello, 

I have RHEL5 and 6. I am just now getting into redhat. So far support has been better than expected. Being thatI only have two production servers, I dont want to go all out on backup software just yet. Whats the cheapest yet reliable way to do a full system back up on my servers just in case my Errata updates go awry? Don't get me wrong they will be important production servers and I will have to test the restore method also. 

Thanks, 

Joseph