When most people think of high availability, they set four nines or less than five minutes of downtime every month as the baseline. But according to Dave Bermingham, Senior Technical Evangelist at SIOS Technology, high availability is more than that.
“When we look at the big picture of any service that needs to be available, there are many chains in that link. We call it the chain of high availability,” says Bermingham. “So you have to look at the big picture.”
He argues that counting on nines is really a measurement that you might be judged against, but really trying to guarantee a level of nines is almost impossible. Because there are so many points in that availability chain that can be a single point of failure. Four nines is certainly a great number to be judged against and to strive for, but overall it doesn’t mean a lot to have just four nines for my database server.
Even with Cloud SLAs (Service Level Agreements), one can’t be fully rest assured as most cloud providers offer four nines on compute, which is only one part of the availability chain (along with network, storage, and the hops between). Bermingham warns, “There are a million points of failure. So, trying to think that my cloud provider offers four nines so I’m covered, you’re kind of fooling yourself there. You have to look at the big picture and do what you can to identify those points of failure, to minimize the potential points of failure and to have a recovery plan, should something happen.”