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Tip of the Day
Language: Web
Expertise: Intermediate
Jun 28, 2017

Calculating Availability

Availability is measured in so-called nines notation, that corresponds to the percentage of time that a service is available. For example, if a service is available 99.9% of the time, we can say that has "three-nines availability". This notation is used to gives us the specific amount of downtime that a service is allowed to have. 

Next are the availability and downtime calculations for 99% availability to 99.999% availability :

99% availability (two-nines):
        * 3.65 days/year (of allowed downtime)
        * 7.20 hours/month
        * 1.68 hours/week
        * 14.4 minutes/day

99.9% availability (three-nines):
        * 8.76 hours/year
        * 43.8 minutes/month
        * 10.1 minutes/week
        * 1.44 minutes/day

99.99% availability (four-nines):  
       * 52.56 minutes/year
       * 4.38 minutes/month
       * 1.01 minutes/week
       * 8.66 seconds/day

99.999% availability (five-nines):
       * 5.26 minutes/year
       * 25.9 seconds/month
       * 6.05 seconds/week
       * 864.3 mimiseconds/day

Octavia Anghel
 
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