Numbers To Know easy
What is the maximum allowed downtime per year for a system targeting '99.9%' (Three Nines) availability?
- A approximately 9 hours
- B approximately 50 minutes
- C approximately 3 days
- D approximately 1 minute
Answer: A. approximately 9 hours
Availability is calculated based on total time. There are 8,760 hours in a standard year; 99.9% availability allows for a 0.1% failure rate, which translates to exactly 8.76 hours of downtime per year. While 'Three Nines' might sound impressive, 9 hours of downtime annually can still represent a significant loss in revenue for a major global platform. Moving to 'Four Nines' (99.99%) drastically reduces this limit to just ~52 minutes per year, requiring much more sophisticated engineering and high-availability infrastructure.
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