Posts in Category: High Availability

Understanding the “Nines of Availability” 

If you’ve spent any amount of time in the tech field you’ve probably heard of the “Nines of Availability”. Availability is usually expressed as a percentage of uptime in a given year. The following table shows the downtime that will be allowed for a particular percentage of availability, presuming that the system is required to operate continuously.

Availability %

Downtime per year

Downtime per month

Downtime per week

90% 36.5 days 72 hours 16.8 hours
99% 3.65 days 7.20 hours 1.68 hours
99.9% ("three nines") 8.76 hours 43.2 minutes 10.1 minutes
99.99% ("four nines") 52.6 minutes 4.32 minutes 1.01 minutes
99.999% ("five nines") 5.26 minutes 25.9 seconds 6.05 seconds
99.9999% ("six nines") 31.5 seconds 2.59 seconds 0.605 seconds
Posted by Brian 11/05/2009 Categories: High Availability