Blog Objective

This is a blog that attempts to make life easier by noting down the author's accrued knowledge and experiences.
The author has dealt with several IT projects (in Java EE and .NET) and is a specialist in system development.

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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