Brian's Blog

items I see across my tribes

Five nines: what does it mean?

April 30
by briancarter 30. April 2009 13:26

 Let us examine the math of it, first. A definition of availability may help: "The percentage uptime achieved per year." Given this definition, the maximum downtime permitted per year can be calculated.

If you want to debate leap years, lost seconds, or other oddities, you are on your own.  The figures below are sufficient to get across the point.

Name Uptime Maximum Downtime per Year 
Six nines  99.9999%   31.5 seconds 
Five nines  99.999%   5 minutes 35 seconds 
Four nines  99.99%   52 minutes 33 seconds 
Three nines  99.9%   8 hours 46 minutes 
Two nines  99.0%   87 hours 36 minutes 
One nine  90.0%   36 days 12 hours 

 

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