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Raid 0: Your data is distributed over two physical disks (which appears to be one large disk to your system). Offers (near) double speed and huge partitions. But it does have it's price: If one of the disks fails all your data is lost.

Raid 1: All your data is written to both disks. Offers very nice secutity against data loss, since one failed disk may simply be replced, but at the cost of much redundancy (you can only use "half" the space you got).
 
RAID 5 is a set of 3 disks or more. You lose the capacity of 1 disks worth of space when in a RAID 5 array. Data is written across all disks in the array, you can lose any 1 disk and not lose your data. You just replace the failed drive and the data is rebuilt based on what's on the other disks in the array.
 
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