Talk:Notification system

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In the Fail-over Scenarios section, had the sentence:

"High availability means that a system must be up and running 99.99999% of the time. "

I changed the percentage to 99.999%. In my experience, the term 'Five nines' availability refers to all the nines, not just the ones to the right of the decimal point. 99.999% availability means you can only have 26 seconds per month, or about 5 minutes per year, of downtime. That is the standard most managers of high availability systems are trying reach when they refer to 'Five nines'. And very few, even high availability systems, get there. Much less 99.99999%. That's about 26 seconds per _year_.

And I messed up my own math there. 99.99999 would be about 3 seconds per _year_. Good luck!

In fact, I just noticed there's a Wikipedia article about this, http://en.wikipedia.org/wiki/The_Myth_of_the_Nines

And, from http://en.wikipedia.org/wiki/Availability:

"Note 2: Typical availability objectives are specified either in decimal fractions, such as 0.9998, or sometimes in a logarithmic unit called nines, which corresponds roughly to a number of nines following the decimal point, such as "five nines" for 0.99999 reliability.

Source: from Federal Standard 1037C in support of MIL-STD-188"

Note that the factor, .99999 ("five nines"), is the same as 99.999 percent.

I'll stop soon. Really.

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