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Unix Backup and Recovery by W. Curtis Preston

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Chapter 6. High Availability

Good backup and recovery strategies are key to any organization in protecting its valuable data. However, many environments are starting to realize that while a system is being recovered, it is not available for general use. With a little planning and financial backing, you can design and implement logical schemes to make systems more accessible—seemingly all the time. The concept of high availability encompasses several solutions that target different parts of this problem.

Tip

This chapter was written by Gustavo Vegas of Collective Technologies, with input from Josh Newcomb of Motorola. Gustavo may be reached at , and Josh may be reached at .

What Is High Availability?

High availability (HA) is defined as the ability of a system to perform its function without interruption for an extended length of time. This functionality is accomplished through special-purpose software and redundant system and network hardware. Technologies such as volume management, RAID, and journaling filesystems provide the essential building blocks of any HA system.

Some would consider that an HA system doesn’t need to be backed up, but such an assumption can leave your operation at significant risk. HA systems are not immune to data loss resulting from user carelessness, hostile intrusions, or applications corrupting data. Instead, HA systems are designed in such a way that they can survive hardware failures, and some software failures. ...

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