Storage management: It's a RAID

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Crossing those Ts

So what's the difference?

A Redundant Array of Independent Drives is a way to make a computer treat a number of physically distinct drives as one big drive. There are several different RAID configurations, each with its own advantages and disadvantages. The configurations mentioned in this review are:

RAID 0: RAID 0 uses the most basic RAID technique, called striping. Each disk's space is split up into stripes of a certain length, which can vary based on different RAID management programs but is always the same within a single RAID. The software then writes to each stripe before moving onto a stripe in the same position on the next drive. So the first stripe on disk one would be followed by the first stripe on disk two, and so on. This allows for maximum capacity equal to the sum of all the drives' capacities. But with RAID 0, if a single drive fails, the entire RAID fails and you will likely lose all your data.

RAID 1: This RAID uses a different technique called mirroring. The disks are paired up and the second disk in each pair is an exact copy of the first. Each pair is treated as a separate drive. This has maximum redundancy, as both drives in a pair would have to fail for that logical drive to fail. However, the capacity is half that of RAID 0.

RAID 1+0 (or 10): This RAID combines the techniques of RAIDs 0 and 1. Each pair of drives is mirrored, and each mirrored pair is striped so that the RAID is treated as one drive. This is just as secure, but also has the halved capacity of RAID 1. The difference is that each pair is not treated as a separate drive, but one contiguous one.

RAID 5: This more secure RAID uses striping but does something different with the stripes. For each set of stripes (such as the first stripe of every disk in the RAID), one of the disk's stripes contains parity data corresponding to the data on the other disks.

The disk that has the parity information alternates with each set of stripes. This has the advantage that if one disk fails, it can be rebuilt completely from the information on the other disks. Still, RAID 5 isn't 100-percent bulletproof in protecting data'only the mirroring of RAID 1 can offer that. But RAID 5 is highly reliable. The advantage it has over RAID 1 is the increased capacity. With only one disk in the array being used for storing parity, the capacity of a five-disk array would be the total size of the remaining four disks.

About the Author

Greg Crowe is a former GCN staff writer who covered mobile technology.


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