99.9% Uptime Guarantee
Uptime is the amount of time that a server has stayed up and running. This is usually listed as a percentage, like "99.9% uptime." Uptime is a great measure of how good a Web hosting provider is at keeping their systems up and running. If a hosting provider has a high uptime percentage, then that means that their servers stay up and running and so any site you host with them should stay up and running too. Since Web pages can't keep customers if they are down, uptime is very important.
But There are Problems with Grading a Web Host on Uptime
The biggest problem with grading a host on their uptime is that you generally have no way to independently verify it. If the host says they have 99.9% uptime, you have to take them at their word.
But there's more to it. Uptime is almost always defined as a percentage of time. But a percentage of what amount of time? If JoeBlos Web Hosting has a 99% uptime, that means they have a 1% downtime. Over the course of a week, that would be 1 hour, 40 minutes, and 48 seconds that their server is down. Averaged over a year, that would mean that your server would be down as much as 87.36 hours per year or over 3 days. Three days doesn't sound like all that much, until you're not making any sales from the website and are receiving calls from the VP (or worse yet, the CEO). And the frantic calls usually start after 3 hours, not 3 days.
Uptime percentages are misleading. As I pointed out above, 99% uptime sounds great, but it could mean a 3 day outage every year. Here are some mathematical explanations of uptimes:
When you're choosing your Web hosting provider, look at their uptime guarantees, I recommend only going with a company that offers a guaranteed uptime of 99.5% or higher. Most offer at least 99% uptime guaranteed.
But Uptime Guarantees Can be Misleading Too
Uptime guarantees are not usually what you might think they are. Unless your hosting agreement is very different from every other hosting agreement I've ever seen, the uptime guarantee works something like this:
We guarantee that if your website goes down for more than 3.6 hours per month in unscheduled outages, we will refund the cost of the hosting for the amount of time you reported and they verified your site was down.
Let's break that down: