Uptime
Uptime is the amount of time an IT service operates without interruption. It is a key metric used to evaluate the reliability of IT systems: hosting, SaaS platforms, networks, and all other systems.
When we use even simple familiar services, such as visiting our favorite website to watch kittens, or call friends, we expect the service to work without interruption at all times. The uptime metric is used to determine how well the service meets these expectations.
What uptime is measured by
Uptime is the ratio of uptime to total observation time. Typically, uptime is expressed as a percentage or net time. For example, an uptime of 99.9% per year means that the service is running 99.9% of the year and its downtime does not exceed 8.76 hours per year.
Ispmanager also displays server uptime. It is located on the dashboard in the System Information section.
Uptime is also measured in minutes, hours, days that the system has been running without a failure. So a server with 30 days of uptime means that the system has been running for 30 days without rebooting or shutting down.
Uptime and SLA
To prove the reliability of their service and make it attractive, providers often offer users a minimum uptime indicator - a guaranteed level of availability (service level agreement, or SLA). For example, 99.99% per year. Depending on the terms of the contract, companies may offer different levels of compensation to customers if uptime falls below the acceptable level.
The opposite concept of uptime is — downtime. Downtime is a period of time when the system was unavailable or did not perform as expected.