If you have heavy-duty storage needs, a RAID (Redundant Array of Independent Disks) is the most cost-effective, mind-easing solution, though it can be a major pain to set up. A RAID is two or more hard drives linked together to function as a single storage device, providing greater capacity, better performance, and automated backups (depending on how it’s configured). You can build a RAID yourself or buy a preconfigured one.
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http://www.macworld.com/article/131186/2009/04/desktop_raid.html