Redundancy is a wonderful way to promote fault tolerance. That is why high-end equipment today comes with dual fans, dual storage controllers and even dual power supplies. But redundancy shouldn't end at the power supply.
One of the classic failure modes for any kind of electronic equipment is to pull the plug. Computer lore is rife with stories about the janitor who brought down a multi-million dollar data center by unplugging a server to plug in his vacuum cleaner, or the office worker who accidentally kicked the plug out of the wall. The stories are silly, but they do happen and they can still shut down a system. Ironically not even a UPS will protect from this kind of accident if the cord gets pulled is the one leading from the UPS to the system.
That is one reason that more and more vendors are offering equipment with dual power cords. If one plug gets pulled, the other can carry the load. Dual cords are available as an option on everything from storage arrays to SAN switches to servers. McData and IBM currently offer the Spereon 4500 Fabric Switch; Stratus offers the ftStorage Fibre Channel Array. It's a relatively low cost bit of added protection.
Ideally, the redundancy doesn't stop at the wall outlet. The cords should be attached to separate circuits on separate master breakers, if possible.
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About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.
This was first published in August 2004