Understanding Availability Nines
Network availability is commonly expressed as a percentage, often referred to by the number of nines. Each additional nine dramatically reduces the allowed downtime.
Downtime = Total_time x (1 - Availability/100)
Annual Downtime = 365.25 x 24 x 60 x (1 - Availability/100) minutes
Annual Downtime = 365.25 x 24 x 60 x (1 - Availability/100) minutes
Moving from 99.9% to 99.99% availability means reducing downtime from 8.77 hours/year to 52.6 minutes/year - a 10x improvement that typically requires significant infrastructure investment.