It's the gold standard of service-level agreements (SLAs): something being available 99.999 per cent of the time (or 'five nines', as those in the trade often call it). But does it really mean anything?
Uptime picture from Shutterstock
Google issued a blog post this morning boasting about the reliability of its Google Apps service. The actual guarantee for Apps is 99.9 per cent uptime (three nines, if you like). For 2012, the figure was 99.983 per cent. That's not quite five nines, but it's rather close, and Google maintains it wants to improve the figure. " We work hard to make sure any disruptions are rare, limited in scale and quickly resolved," the post notes.
That's good news for customers. However, it raises the first important point about high availability: it always costs more. Google makes no such guarantee about the availability or reliability of its free services (though the underlying infrastructure is used by both Google Apps and plain od vanilla Gmail). That doesn't mean lots of people don't use them very happily without incident. It just means they don't have much recourse when things go wrong.
The second point is this: downtime in itself is not always a bad thing. Unplanned downtime can be a bad thing, and in an era where many businesses expect to sell goods on their sites 24/7, it can make sense to try and minimise it. But the world won't stop turning if you have an occasional outage and tell people about it.
The obvious proof? Apple. Every time there's a major product announcement, its online store is taken offline. That's no credit to Apple's ability to develop web services (an area where it lacks serious smarts). But judging from its financial results, it hasn't been a business-crippling problem.