The Mac Pro and Xserve support OS X Lion Server and contain multiple drive bays that give you the option to set up multiple drives to work together as a RAID (Redundant Array of Individual Disks) to increase performance or protect data, or both. You can also plug an external RAID box into a FireWire 800 or Thunderbolt port. Apple software supports four types of RAID:
RAID 0 isn’t actually redundant, despite the name. RAID 0 uses a striping technique to make multiple hard drives work together as a single, fast, large hard drive. Data from a file is fragmented and written on multiple drives.
When reading the file, the system can read the fragments from all the drives simultaneously, greatly increasing performance. RAID 0 also lets you create a very large single volume for storing giant files, such as video. If one of the drives in a RAID fails, all the data is lost. RAID 0 requires two hard drives minimum.
RAID 1 uses a mirroring technique to write the same data to two drives simultaneously. If one drive fails, the other drive still contains all the data. RAID 1 requires two hard drives minimum.
RAID 5 makes more efficient use of hard drive space than RAID 1 and has better performance. The drawback to RAID 5 is that it requires three hard drives minimum.
RAID 0+1 first creates a RAID 0 striped array — a very large volume from two hard drives, giving you the fast performance. RAID 0+1 then mirrors the first array with a second striped pair, giving you the redundancy. The drawback is that it requires at least four hard drives.
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Source:http://www.dummies.com/how-to/content/raid-storage-for-lion-server-hardware.html
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