Practical Monitoring

Appendix B. Availability Chart

As mentioned in Chapter 4, Table B-1 is a chart of availability numbers. It’s a great reference for how much downtime is allowed within a given availability target.

Table B-1. Availability (chart thanks to Wikipedia)

Availability %	Downtime per year	Downtime per month	Downtime per week	Downtime per day
90% (“one nine”)	36.5 days	72 hours	16.8 hours	2.4 hours
95% (“one and a half nines”)	18.25 days	36 hours	8.4 hours	1.2 hours
97%	10.96 days	21.6 hours	5.04 hours	43.2 minutes
98%	7.30 days	14.4 hours	3.36 hours	28.8 minutes
99% (“two nines”)	3.65 days	7.20 hours	1.68 hours	14.4 minutes
99.5% (“two and a half nines”)	1.83 days	3.60 hours	50.4 minutes	7.2 minutes
99.8%	17.52 hours	86.23 minutes	20.16 minutes	2.88 minutes
99.9% (“three nines”)	8.76 hours	43.8 minutes	10.1 minutes	1.44 minutes
99.95% (“three and a half nines”)	4.38 hours	21.56 minutes	5.04 minutes	43.2 seconds
99.99% (“four nines”)	52.56 minutes	4.38 minutes	1.01 minutes	8.64 seconds
99.995% (“four and a half nines”)	26.28 minutes	2.16 minutes	30.24 seconds	4.32 seconds
99.999% (“five nines”)	5.26 minutes	25.9 seconds	6.05 seconds	864.3 milliseconds
99.9999% (“six nines”)	31.5 seconds	2.59 seconds	604.8 milliseconds	86.4 milliseconds
99.99999% (“seven nines”)	3.15 seconds	262.97 milliseconds	60.48 milliseconds	8.64 milliseconds
99.999999% (“eight nines”)	315.569 milliseconds	26.297 milliseconds	6.048 milliseconds	0.864 milliseconds
99.9999999% (“nine ...