I was curious about how many 9s in typical service level agreements translates into how much actual time is allowed by each level of guarantee. A quick Google didn’t yield any quick references, so I turned to Excel and am including it here for future reference. For example, if a service provider offers three 9s, or 99.9% uptime SLA guarantee, how much does that actually allow in terms of time unavailability? Calculated for a regular 365-day year (leap years get you a couple extra seconds), here are the results:
|# of 9s||SLA Guarantee||Minutes of Downtime||Hours of Downtime|
So essentially what we’re looking at is that with a 99% guarantee, the provider is allowed a little over 3.5 days of downtime per year, a 99.99% SLA is allowed a little under 1 hour, and seven 9s (99.99999%) guarantees you just 3 seconds of downtime per year. Interesting from a customer perspective, and even more interesting from a provider’s perspective.