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RAID Benefits

Alright, let's take a look at the good stuff first. :^) RAID really does offer a wealth of significant advantages that would be attractive to almost any serious PC user. (Unfortunately, there are still those pesky costs, tradeoffs and limitations to be dealt with... :^) ) The degree that you realize the various benefits below does depend on the exact type of RAID that is set up and how you do it, but you are always going to get some combination of the following:

• Higher Data Security: Through the use of redundancy, most RAID levels provide protection for the data stored on the array. This means that the data on the array can withstand even the complete failure of one hard disk (or sometimes more) without any data loss, and without requiring any data to be restored from backup. This security feature is a key benefit of RAID and probably the aspect that drives the creation of more RAID arrays than any other. All RAID levels provide some degree of data protection, depending on the exact implementation, except RAID level 0.
• Fault Tolerance: RAID implementations that include redundancy provide a much more reliable overall storage subsystem than can be achieved by a single disk. This means there is a lower chance of the storage subsystem as a whole failing due to hardware failures. (At the same time though, the added hardware used in RAID means the chances of having a hardware problem of some sort with an individual component, even if it doesn't take down the storage subsystem, is increased; see this full discussion of RAID reliability for more.)
• Improved Availability: Availability refers to access to data. Good RAID systems improve availability both by providing fault tolerance and by providing special features that allow for recovery from hardware faults without disruption. See the discussion of RAID reliability and also this discussion of advanced RAID features.
• Increased, Integrated Capacity: By turning a number of smaller drives into a larger array, you add their capacity together (though a percentage of total capacity is lost to overhead or redundancy in most implementations). This facilitates applications that require large amounts of contiguous disk space, and also makes disk space management simpler. Let's suppose you need 300 GB of space for a large database. Unfortunately, no hard disk manufacturer makes a drive nearly that large. You could put five 72 GB drives into the system, but then you'd have to find some way to split the database into five pieces, and you'd be stuck with trying to remember what was were. Instead, you could set up a RAID 0 array containing those five 72 GB hard disks; this will appear to the operating system as a single, 360 GB hard disk! All RAID implementations provide this "combining" benefit, though the ones that include redundancy of course "waste" some of the space on that redundant information.
• Improved Performance: Last, but certainly not least, RAID systems improve performance by allowing the controller to exploit the capabilities of multiple hard disks to get around performance-limiting mechanical issues that plague individual hard disks. Different RAID implementations improve performance in different ways and to different degrees, but all improve it in some way. See this full discussion of RAID performance issues for more.

Next: RAID Costs

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