Why 100% uptime often ISN’T 100% uptime

Here’s a little-known fact: Even when your hosting provider says it has provided 100% uptime, that doesn’t necessarily mean that your site hasn’t had any downtime.
Why is that? Because many hosting providers calculate their uptime in ways that aren’t intuitive from a customer perspective, ways that sometimes exclude certain downtime.
When hosting providers calculate their uptime (normally on a monthly basis), they follow a set of rules that are usually lined out in their terms of service, i.e. in the fine print. Here are a few common rules that some hosting providers use:

  • Not counting maintenance downtime – If a hosting company interrupts the service for two hours to perform planned maintenance, this will often not be counted into the uptime percentage. In other words, when it’s time to calculate the uptime percentage for that month, any planned service interruptions simply aren’t counted.
  • Not counting shorter periods of downtime – Perhaps the most prominent example of this is Google Apps (including Gmail) which won’t count any downtime that is shorter than 10 minutes. So if Gmail were to be down five different nine-minute periods, you’d have had 45 minutes of actual downtime, but no official downtime as far as Google is concerned.
  • Only counting network downtime – This one is especially common among dedicated hosting providers. Individual server failures that may or may not affect your site aren’t counted. To be fair, for dedicated hosting providers it would be difficult to guarantee anything else when the customer has control over the server.

These methods make it easier for hosting providers to fulfill their uptime goals, for example not going below 99.9% uptime in a month. If you have a service level agreement with your hosting provider it might be a good idea to take a close look at how its uptime percentage is calculated. Be sure to use our server uptime service to make sure this doesn’t happen to your server!
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  1. My ISP is one of those that don’t include short downtimes at all. And by short i mean up to two hours.. Two months ago the network was down for six hours and in the following report it stated that the downtime was only 30 seconds! I phoned during that blackout for four of my friends from the same area and ISP and they confirmed that. They also disconnected and connected my account and charged for 30€ it when my payment was overdue. The connection was out for ten seconds…

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