Summary

Redundancy is one of the guiding principles for storage networks. Of the three forms of redundancy—duplication, parity, and delta—duplication as instantiated in mirroring and backup products has been the most heavily implemented over the course of several decades.

Mirroring is a simple concept developed for online, real-time duplication of storage I/O commands to two targets in a mirrored pair. The location of the mirroring operator can have a significant impact on the overall availability of a system and its data. It is often implemented at multiple levels to provide protection from different kinds of threats.

Often mirroring is confused with two other related and complementary redundancy applications: multipathing and remote copy. It's ...

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