How do we calculate the uptime of 24/7 website?

Question

When companies come forward and claim 99.98%, how do they come to that number? Is that the only QoS parameter or are there any other useful and important parameters?

Answer 1

There are several useful QoS parameters, although not all are as easily measured as e.g. 99.98% uptime, which is easily derived - 99.98% of the time, your server is available. Other metrics:

• What sort of bandwidth do they support? How about if it's a shared pipe and they've multiple high-volume clients? You're unlikely to get an honest answer to this from the vendor.
• If you're on a shared host, what sort of competition for resources will you have on the box? Again, this is competitive information, so you're unlikely to get an honest response.
• How independent is each application? i.e. if another application on a co-hosted box loops MySQL, will your app suffer?
• How often do they upgrade dependencies, and does that affect their 99.98% uptime?

Then there are the fluffy not-entirely-QoS related hosting problems:

• Will they do your backups etc.?
• How responsive are they to queries? Do they have a guaranteed response time e.g. 3 hours from first email to first response, 24/7?
• Are they efficient? Have they resolved issues within a useful timeframe? A quick response-time is nice and feelgood, but if they don't fix the problem, that's not quite so good!
• Are they patient with you when you suggest issues, but due to your own technical background are slightly off-base? :)

Answer 2

That means your downtime is going to be roughly 2 hours per year. Out of 8760 hours, it's safe to assume your website isn't going to lose much traffic or business because of problems in their hosting.

I would look at testimonials or search online for reviews of the company for anything else.

Answer 3

Uptime is one quality of service figure. Other interesting figures are "mean time to fix", "mean time between failures" and other service restoration figures. Ideally, there would be people awake and alert 24/7 to fix faults, but most places will (at best) have alert and awake people monitoring the service 24/7 and have on-call engineers to do the actual fix (at least if it's a more complicated one), so knowing how out-of-hours service (IF they will tell you) is also a factor in choosing a provider.