High availability is often expressed as “nines”, or the percentage of availability in a year. Six nines is 99.9999% uptime or no more than 31.5 seconds of downtime in a year.
Achieving “Six Nines” When You Launch
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
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%
How to Achieve Six Nines in 2009
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:
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Q: How can you tell when you are working in a high reliability organization (HRO)? A: I like to use the 5 Principles of HRO’s as codified by Karl Weick and Kathleen Sutcliffe in their book Managing The Unexpected: Resilient Performance in an Age of Uncertainty.
- Preoccupation with Failure: We were continuously on the lookout for what could go wrong and ways to spot weak signals and small failures early so we could act on them and take corrective actions.
- Reluctance to Simplify: Complex problems don’t always have simple solutions, yet it can be comfortable to jump on the last solution that worked well or the one that most readily comes to mind. We created an environment where diverse opinions were sought out to help balance biased decisions.
- Sensitivity to Operations: Plans are necessary, but operations will vary, so crews need to pay attention to operations as they unfold and make dynamic adjustments based on the actual (not planned) conditions.
- Deference to Expertise: Marine Aviation units are complex organizations, with multiple different job duties and roles. For example, there are mechanics, administrative personnel, intelligence personnel, and aircrew. Everyone has his or her job to do. Deferring to the experts means ensuring there are competent Marines who can do their jobs and then trusting them. This is often referred to as “Special Trust and Confidence” and in many cases this can be seen between Officers and Staff Non-Commissioned Officers, who are trusted advisors.
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- Fred Brooks’ “No Silver Bullet” Revisited
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