Hosting reliability and uptime

Hosting reliability and uptime

Hosting uptime refers to the percentage of time the host is accessible via the internet. Many providers state that they aim for at least 99.9% uptime (roughly equivalent to 45 minutes of downtime a month, or less), but there may be server restarts and planned (or unplanned) maintenance in any hosting environment, which may or may not be considered part of the official uptime promise. Many providers tie uptime and accessibility into their own service level agreement (SLA). SLAs sometimes include refunds or reduced costs if performance goals are not met.

Uptime is a measure of the time a computer system has been "up" and running. It came into use to describe the opposite of downtime, times when a system was not operational. The uptime and reliability of computer and communications facilities is sometimes measured in nines (similar to the unit of metallic purity). "Five nines" means 99.999% availability, which translates to a total downtime of approximately five minutes and fifteen seconds per year.

\	Total downtime (HH:MM:SS)
Availability	per day	per month	per year
99.999%	00:00:00.9	00:00:26	00:05:16
99.99%	00:00:09	00:04:23	00:52:36
99.9%	00:01:26	00:43:50	08:45:57
99%	00:14:24	07:18:17	87:39:30

It is often used as a measure of computer operating system reliability and stability, in that this time represents the time a computer can be left unattended without crashing, or needing to be rebooted for administrative or maintenance purposes. Conversely, long uptime can indicate negligence, because critical updates can sometimes require reboots.