Storage Tip: When Is a Disaster Not a Disaster?

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What seems to be the problem? Okay, I confess. I chose the title because it was catchy. However, it does describe a very real problem that many organizations face. When do you consider an event a disaster? Why must you distinguish between problems that are disasters and those that are non-disasters, especially since a non-disaster could still be a serious problem?



As we shall see, enterprises must be able to make a clear distinction between types of downtime causing or threatening events for planning and provisioning purposes. The response to each type of situation is different. Understanding when a real disaster occurs is easy (a hurricane such as Katrina that renders a data center inoperable either for an extended period of time or permanently), but is a fire that destroys only a single disk array (albeit one with a key application on it) a disaster?



What do you need to know? The basic distinction is that a non-disaster problem is an operational recovery problem and a disaster is a disaster recovery (DR) problem. (Although it is not necessary, you may want to review the storage tip "Data Protection: Getting Back to First Principles." A disaster occurs when a downtime-threatening or causing event forces you to failover to a remote site, either your own or that of a third party, for an extended period of time. Every other event is an operational problem, i.e., a non-disaster.



What happens if I lose that key disk array at a local site (say to fire or two disk failures) and have to failover to the DR site? Isn't that a disaster? Not if the failure is isolated to a single array and not the whole data center. You could theoretically have placed the mirrored array at the local site. More importantly, your basic management team, policies, and procedures are still in place at the local site. Responsibility has not been transferred to the remote site except for running the mirror copy of the affected array as the production copy.



What are the tradeoffs? Knowing the difference between an operational problem and a disaster is essential as they are treated differently (see Table).



Table: Differences between Operational Recovery and Disaster Recovery

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