The LaCie 5big Thunderbolt really shows off the excellent performance you can get with the Thunderbolt interface. By just connecting one cable you have immediate access to 20 TB of really fast storage. It's perfect if you work with large photos and videos. If you want safe and secure back-up, then a RAID 0 external hard disk is not the best solution. While you could of course put two disks in RAID 1 (mirror), there are more affordable options for good back-up devices.
Price is an important variable here, since the 5big Thunderbolt isn't sold without hard disks. The LaCie 5big Thunderbolt 10TB costs $1,100 and the 20TB model costs $1,921. If that's within your budget, you got yourself easy to use super-fast multi-terabyte storage.