I have a centos 6.5 server set up, I found the easiest way to backup with peace of mind is to clone your hard drive.
I connect a second hard drive to my system "the one I want to clone too". Same size as original source hard drive in my case 2TB drives.
I boot off of a Knoppix 7.2 live cd. I start a terminal session as su
then I type:
dd if=/dev/sda of=/dev/sdb bs=4096 conv=notrunc,noerror
DON'T MIX THIS UP!!!! MAKE SURE YOU KNOW WHICH DRIVE IS THE SOURCE AND WHICH IS THE TARGET
if=/dev/sda : Input disk (source)
of=/dev/sdb : Output disk (destination)
It takes approx 5 hours so I start the clone before I plan on going to bed
It works every time. I test it by booting off the clone drive.
I have successfully cloned the same size hard drives while linux was running from a terminal with the above command.
but it is safer if you just do the cloning from the live cd since both drives will be unmounted.