Uptime; what do all those 9’s mean?

Uptime means the time a compute or system is being used without any problems. But how much time is that when 99.99% is promised?

According to a dictionary, uptime means:

the period of time when a computer, system, etc.

is being used without any problems.


What that means in real time:

UptimeTotal downtime per year
99.00000%3 days, 15 hours and 39 minutes
99.90000%8 hours, 45 minutes and 56 seconds
99.99000%52 minutes and 35 seconds
99.99900%5 minutes and 15 seconds
99.99990%31 seconds
99.99999%3 seconds

(source: Matt Rickard – @mattrickard at Twitter)

So this is downtime per year!

At Fuga you get a 99.99% uptime SLA,

although we are actually between 99.99% and 99.999%. But let’s assume 2×9 behind the dot:

52 minutes and 35 seconds per year

is 3155 seconds per year

Divide by 365 days makes (rounded up) 8.64383 seconds per day

x7 = 60.50681 seconds per week

That’s an itsy bitsy teenie weenie more than 1 minute of downtime per week!

(source: Matt Rickard – @mattrickard at Twitter) For every extra 9 after the dot you should take into account a multiplication of 10 for the costs. If you know what it will cost you to be down for 1 minute, you can make an offset against the costs you will incur for wanting that extra 9 behind the dot in your SLA. Because everything is possible, we know that, but these kinds of considerations deserve a fair calculation.


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