There are a number of measures used to assess and report the performance of a service or component in respect of it being available.
Availability is defined as the ability of a service or component to perform its required function when needed. It is usually calculated as a percentage.
Reliability is a measure of how long a service or component can perform its required function without interruption. It is calculated using the metrics Mean Time between System Incidents & Mean Time to Restore Services.
Maintainability is a measure of how quickly a service or component can be restored to its working state after a failure.
Note: Availability, reliability and maintainability measures all need to include a time interval, typically hours.
Serviceability is a measure of a third-party provider’s ability to meet their contracted support commitments in terms of availability, reliability and maintainability.
The Formulae used to gather metrics related to Availability Management are as follows:
Each of these measures is subject to scrutiny and appropriate actions by Availability Management in order to minimize interruptions to services and service outages both proactively and reactively. The extent to which a service is vital to the business will determine the level of availability and resilience applied. Those business functions considered very important are known as Vital Business Functions (VBFs) and it is these on which Availability Management will be most focused.
In relation to the expanded Incident lifecycle, the following metrics are useful:
• Incident response time
• Incident repair time
• Incident recovery time
• Incident restoration time
• Incident resolution time
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