Achieving “Six Nines” When You Launch
Add comment September 1st, 2009
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