I don't believe that there is any such thing as 100% uptime. I also believe that it is irresponsible of vendors to claim that there is. Can they categorically guarantee that their firmware/software/microcode is absolutely bug-free? I doubt it. Are its disks in a single container (array/box)? If so, then surely an external event such as a water leak or a ceiling collapse would bring the box down. An extended power failure will almost always cause downtime.
What you'll find is that vendors who do claim 100% are forced by its (wise) attorneys to put all sorts of exclusions in its contracts. Read them carefully. Remember, too, that your system consists of many components of which the storage subsystem is only one. The only availability metric that matters is what the users see. Will users see 100% uptime? Not in this lifetime.
Evan L. Marcus
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This was first published in October 2002