Ask HN: What does 99.999% reliably actually mean?
I always thought of it as some marketing thing but apparently it maps to uptime/downtime. Anyone care to explain the math?
In comparison, if a service is only 99% reliable, it can be down for a total of 3.65 days per year.
The availability of your service depends on several factors, such as the availability of your servers, the availability of network connectivity, whether you have an uninterruptible power supply, etc.
Reliability is important to different people for different reasons. If Google search goes down for an hour, it's a mild inconvenience for any given user, but Google would lose a lot of revenue. If the phone system goes down for an hour, lots of people could die because they couldn't call for emergency services.
e.g. "We will give you $1 per minute for the first 5 minutes of downtime, $10 per minute for the next 50, $100 per hour thereafter"
Or something, I just made that rate up but that's the idea.