25 November 2011

Service Level Agreement (SLA) and Number of 9s

To commit to memory, SLA 9s and acceptable unscheduled downtime:

Availability %Approximate downtime/ year
9050,000 minutes (800 hours)
995,000 minutes (80 hours)
99.9500 minutes (8 hours)
99.9950 minutes (1 hour)
99.9995 minutes
99.99990.5 minutes


In more details, for reference:

Availability %Downtime/ yearDowntime/ month*Downtime/ week
90% (“one 9”)36.5 days72 hours16.8 hours
95%18.25 days36 hours8.4 hours
98%7.30 days14.4 hours3.36 hours
99% (“two 9s”)3.65 days7.20 hours1.68 hours
99.5%1.83 days3.60 hours50.4 minutes
99.8%17.52 hours86.23 minutes20.16 minutes
99.9% (“three 9s”)8.76 hours43.2 minutes10.1 minutes
99.95%4.38 hours21.56 minutes5.04 minutes
99.99% (“four 9s”)52.56 minutes4.32 minutes1.01 minutes
99.999% (“five 9s”)5.26 minutes25.9 seconds6.05 seconds
99.9999% (“six 9s”)31.5 seconds2.59 seconds0.605 seconds

* Assume a 30-day month.

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