This one is popular with our photography clients...the drobo Storage Robot:

From the manufacturer:

Drobo is the world's first storage robot, providing fully automated, infinitely expandable storage that safeguards against drive failure and data corruption.

Fully automatic protection: Drobo is self-healing; when a hard drive fails, it reconfigures data to ensure it is once again protected - all without any human intervention.

Infinitely expandable capacity: Drobo is self-improving; just add a new drive, or upsize a smaller one, and you'll instantly increaseoverall protected capacity without needing to do anything else.

Effortless storage management: Drobo is self-aware, knowing where your data is and how to heal or improve itself in the event of trouble - Drobo takes the pain out of managing large amounts of data.

System requirements: Apple Macintosh OS-X 10.4 or greater, Microsoft Windows 2000, 2003, XP or Vista.

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