Service level objectives

Service level objectives (SLOs) are a key element of a service level agreement (SLA) between a service provider and a customer. SLOs are agreed as a means of measuring the performance of the Service Provider and are outlined as a way of avoiding disputes between the two parties based on misunderstanding.

There is often confusion in the use of SLA and SLO. The SLA is the entire agreement that specifies what service is to be provided, how it is supported, times, locations, costs, performance, and responsibilities of the parties involved. SLOs are specific measurable characteristics of the SLA such as availability, throughput, frequency, response time, or quality.

The SLO may be composed of one or more quality-of-service measurements that are combined to produce the SLO achievement value. As an example, an availability SLO may depend on multiple components, each of which may have a QOS availability measurement. The combination of QOS measures into an SLO achievement value will depend on the nature and architecture of the service.

In "Foundations of Service Level Management" (2000), Rick Sturm and Wayne Morris argue that SLOs must be:

* Attainable
* Measurable
* Understandable
* Meaningful
* Controllable
* Affordable
* Mutually acceptable

SLOs should generally be specified in terms of an achievement value or service level, a target measurement, a measurement period, and where and how measured. As an example, "90% of calls to the helpdesk should be answered in less than 20 seconds measured over a one month period as reported by the ACD system". Results can be reported by the percent of time that the target answer time was achieved compared to the desired service level (90%).