If a service provider is offering 99 percent uptime, that’s 2 nines of uptime. It’s really telling its customers that, on average, they’ll experience just over 7 hours of downtime in any given month. Is that enough? It depends; it might be good enough for workloads that aren’t critical to enterprise survival, but it’s woefully lacking for critical workloads.
But what exactly does Microsoft’s “99.9-plus” percent uptime statement mean — 99.9001 or 99.999? There’s a huge difference. Let’s do some quick math:
- 99.9% uptime is 8.77 hours of downtime per year
- 99.99% uptime is 52.60 minutes of downtime per year
- 99.999% uptime is 5.26 minutes of downtime per year
For many businesses, I guess 99.9% uptime is quite good.