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FIGURE 9.3 How disk striping works

Each disk holds a piece of the original information.

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Striping data across multiple disks improves only performance; it does not improve fault tolerance. To add fault tolerance to disk striping, it is necessary to use parity. Disk striping is also known as RAID level 0.

Parity Information

Parity, as it relates to disk fault tolerance, is a general term for the fault tolerance information computed for each chunk of data written to a disk. This parity information can be used to reconstruct missing data should a disk fail. Striping can use parity or not, but if the striping technology doesn’t use parity, you won’t gain any fault tolerance. When using striping with parity, the parity information is computed for each block and written to the drive.

The advantage to using parity with striping is gaining fault tolerance. If any part of the data gets lost or destroyed, the information can be rebuilt from the parity information. The downside to using parity is that computing and writing parity information reduces the total performance of a disk system that uses striping. The parity information also reduces the total amount of free disk space.

Redundant Array of Inexpensive (or Independent)

Disks (RAID)

RAID is a technology that uses an array of less expensive hard disks instead of one enormous hard disk and provides several methods for writing to those disks to ensure redundancy. Those methods are described as levels, and each level is designed for a specific purpose:

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