Uptime

Uptime refers to the amount of time that a site or server is available or responsive to web requests. The Internet never sleeps, which means your web site needs to be up every second of every hour of every... well, you get the idea. A visitor could be arriving at your site's home page at any time of the day or night, so a web host with a high uptime percentage is critical.

Advertised Uptime

Nearly all web hosts will advertise and guarantee a "99.9%" or higher uptime percentage. However, these guarantees are about as trustworthy as a used car salesman, not very! There are two main things to look out for. Firstly, often the uptime advertised will be Network Uptime rather than server uptime, so if your server goes down, but there network is still online, they don't class this as downtime. Secondly, the hosting company will generally only use it's own data to work out downtime and therefore and refunds. As you can imagine their downtime figures will often be less than you might be monitoring.

Web hosts that operate their own datacentres and have redundant networks (more than one data line to the internet) will be more reliable than a web host that is running only a single data line.

Independant Monitoring

If you have already signed up for a web host you can use a 3rd party to constantly monitor your site's uptime and be instantly notified by email if your web site ever becomes unresponsive. InternetSeer provides a free monitoring system that will check your web site every 60 minutes. If your web site needs to be monitored more closely, both Alertra or InternetSeer have pay for monitoring plans that are very thorough. If your site goes down for considerable lengths of time and you wish to seek refunds, this data will help your case.