Here's an exemplary discussion and guide, co-developed with the US Library of Congress and the American Society of Media Photographers:
There are loads "solutions" in the marketplace to address the task but following the 3-2-1 method will help filter the marketing noise from what method works best for your individual needs.
Backup, Redundancy, Archive, Availability, Hardware RAID, Software RAID, Uptime, Offline, Recovery Time, Disk Images, NAS, File Server, Backup Server, Data Migration, File Corruption, Bit-Rot, Snapshots, ZFS... oh, how the subject is vast and the options are plentiful (dizzying?).
What matters most is identifying your specific needs, creating a backup strategy to match your comfort and risk scenario, then picking the appropriate methods (see guide above). Armed with that in mind, you know the risk, reward, and expectation behind your backup approach.
Also, for those who haven't seen it, I suggest looking at this article from Small Net Builder on RAID. It suggests where and when they think it's appropriate.
Again, everybody's needs are unique. A 60 TB rSync'd backup solution makes a lot of sense to some people, while a humble external drive, thumb drive, and a free Mozy, Carbonite, or Skydrive account might be the perfect fit for others.
Simply put, learn each method's risk/benefit on your own timetable. It's a whole lot easier than a crash course when you've lost those precious bits and bytes....
...and you need the free resources or paid services from this site I found for my sister,