Part 1 – a continuos onsite backup. Since I work in an Apple world the answer to this is easy. Time Machine comes with OS X. Hook up an external hard drive and let Time Machine go to work. Time Machine runs every hour and backups only the files that have changed. I typically get someone an external hard drive, such as this one that is twice the size of the source drive. So if your internal hard drive is 1TB, get a 2TB Time Machine drive. If you are in an office with a server, OS X server allows for you to back up client machines to the server. I find that backing up like that causes issues and slows down networks. Think about having 20 computers all backing up every hour. You could crash an office network with that. You should still have a fileserver – but for other reasons.
Part 2 – a onsite sync. I typically use this for servers. The Mac Mini server has 2 internal hard drives, and most of my clients are not using up all the space on the first one – so I setup a nightly clone to the 2nd drive. I use software like Carbon Copy Cloner to run a nightly clone.
Part 3 – offsite backup. Look, let’s be honest here things happen. Machines are stolen, there’s a fire, etc. I setup an offsite backup for clients. Either to my own backup systems, or for some home users I set them up with Backup Blaze. Both my own, and Backup Blaze do continuos offsite backup, so if anything happens you will have all of your data safe somewhere else.
At Virtua Computers we use Watchman Monitoring to let us know if a client’s backups are not running properly. It would be a horrible thing to setup all three systems and then have them all fail before a catastrophe.
In this day of technology there is no reason why you shouldn’t be able to sleep knowing your data is safe and secure, and using all three methods mentioned above you will be able to. That and maybe some ZzzQuil.