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The strategy of redundancy is to make a copy of everything, said analyst Jon Toigo. It can mean setting up a backup set of servers, or even creating a complete duplicate of an organization's data center.
"If we have more money than common sense, then we build one-for-one replication somewhere else … so every write that is made to the database here is made to the database there. If the system goes down, the whole workload transfers to the second system," Toigo told the audience at his recent Storage Decisions presentation.
The process is expensive -- not just in the costs involved in building a backup data center, but you need people at the other site to ensure the system works, that every write made in the primary data center is duplicated at the backup site, and any configuration changes that occur at the primary site are duplicated at the backup site.
"It's one of the methods for ensuring the continuity of a system, and it's one of a laundry list menu of options that are available. Full redundancy also happens to be [one of] the most expensive strategies ever thought up for surviving a disaster," he said.
Toigo is the head of the analyst firm Toigo Partners International and chairman of the Data Management Institute.
A less ambitious -- and less costly – measure is relying on backup servers to take over your organization's environment, but that remain idle until needed. He called this "active-passive redundancy" as opposed to the active-active approach of full redundancy outlined above.