99.99% availability是什么意思

1: 99.99%

 

4个9 (four nines) = 99.99% availability

 

a year has 3600*12*365 = 31536000 seconds.

 

(a year) * 99.99% = 31536000 * 99.99% = 31532846.4 seconds.

 

the rest value = 31536000 - 31532846.4 = 3153.6 seconds = 52.56 minutes ~= 1 hour.

 

 

2: 99.999%

 

5个9 (four nines) = 99.999% availability

 

a year has 3600*12*365 = 31536000 seconds.

 

(a year) * 99.999% = 31536000 * 99.999% = 31535684.64 seconds.

 

the rest value = 31536000 - 31535684.64 = 31535684.64 seconds = 5.256 minutes.

 

 

FYI

http://en.wikipedia.org/wiki/Myth_of_the_nines