Achieving “Six Nines” When You Launch

Written by Sean Murphy. Posted in skmurphy

High availability is an increasing requirement for SaaS vendors. Availability is often expressed at “nines”, or the percentage of availability in a year. The following handy table gives you a quick decode to the most common nines.

“Number of Nines” Availability as a Percentage Max Time in a Year
Three Nines 99.9% 8.76 hours
Four Nines 99.99% 52.6 minutes
Five Nines 99.999% 5.26 minutes
Six Nines 99.9999% 31.5 seconds

Note that “six sigma” is normally defined to allow a process variation of plus or minus 1.5 sigma so that it’s actually 4.5 sigma in a “normal distribution” which is 99.99966 which is pretty close to “six nines.” A true “six sigma” is “nine nines” or 99.9999999%

I was talking to a SaaS startup planning to launch this month and I suggested that they could achieve six nines if they launched at the right time this month:

9:09:09 9/9/9

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