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HP-UX System Administrator's Guide: Routine Management Tasks: HP-UX 11i Version 3 > Appendix A Using High Availability Strategies

Using Disk Arrays


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A disk array consists of multiple disk drives under the command of an array controller. The disk array incorporates features that differentiate it from traditional disk storage devices.

Most types of disk arrays provide for one of two possible options for protecting data in the event of a disk failure. This becomes more and more important as the number of disks on a system increases, since the chance of a disk failure also increases. Normally, a disk crash brings the system down or prevents access to data, removing it from service until the problem is located and repaired, and the data is reloaded.

The first kind of data protection is called data encoding. When a disk drive fails, the array controller generates encoded data, which is similar to parity or checksum calculations. This allows missing user data to be reconstructed using a mathematical formula to rebuild lost data. As a result, the data remains accessible and the system remains up and running without suffering any downtime.

The second method of data protection utilizes hardware mirroring as a means of providing high data availability by duplicating data on redundant disk drives. As a result, failure in one disk still allows access to the data on an alternate disk.

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