How Many Nines?

Sat, 24 Nov 2007 14:57:35 GMT

Quite often, when we talk about server up-time, we talk about how many nines. The nines indicate uptime. One nine uptime means 90% up-time. Two nines means 99%. Three nines 99.9%. And so one.

The truth is that almost every application is exactly 1 nine. In order to be less than 1 nine, you have to be down for 72 hours in one month. I suspect that happens to many applications, but not month-after-month. In order to be 2 nines, you have to be down for less than 7 hours per month (3 nines is less than 1). If I look at websites I use, almost all of them are down for at least 7 hours per month, but rarely 72. I don't have any stats, but I suspect that 80% of the websites have 1 nine up-time.

Conclusion: We need a new scale. 98% up-time is very good for a website. 91% is very bad. Yet, both are the same nines.

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How Many Nines?