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Five Nines
Posted on January 10th, 2009 No commentsFor many IT folks, the holy grail of high availability is “five nines”. This means that over a particular period of time (usually one year), they will be able to achieve 99.999% availability for a particular service (such as email).
Availability % Downtime per year Downtime per month Downtime per week 90% 36.5 days 72 hours 16.8 hours 95% 18.25 days 36 hours 8.4 hours 98% 7.30 days 14.4 hours 3.36 hours 99% 3.65 days 7.20 hours 1.68 hours 99.5% 1.83 days 3.60 hours 50.4 minutes 99.8% 17.52 hours 86.23 minutes 20.16 minutes 99.9% 8.76 hours 43.2 minutes 10.1 minutes 99.95% 4.38 hours 21.56 minutes 5.04 minutes 99.99% 52.6 minutes 4.32 minutes 1.01 minutes 99.999% 5.26 minutes 25.9 seconds 6.05 seconds 99.9999% 31.5 seconds 2.59 seconds 0.605 seconds The problem is that each additional nine costs quite a bit more money than the previous one, and at some point the person signing the checks is going to put away their pen. So, the trick lies in first determining what range of availability is desired, then assigning a dollar value to each level of availability, and then finding a balancing point between availability requirements and your budget.
