SollVerfügbarkeit

SollVerfügbarkeit, often written with a hyphen as Soll-Verfügbarkeit, is a planning target for the availability of a system or service. It specifies the desired proportion of time a system should be operational within a defined period, such as a month or a year. The concept is used in reliability engineering, capacity planning and service level agreements to set clear expectations for stakeholders and to guide maintenance scheduling and resource allocation.

Soll-Verfügbarkeit is distinguished from Ist-Verfügbarkeit, which is the actual, measured availability. In practice, planned downtime for maintenance, upgrades or other approved interruptions is commonly excluded from the Soll-Verfügbarkeit, whereas the Ist-Verfügbarkeit reflects the real-time performance, including any unplanned outages. The relationship between the two is central to performance assessment: a system is regarded as performing well when Ist-Verfügbarkeit meets or exceeds the defined Soll-Verfügbarkeit.

Calculation and use are typically straightforward: the Soll-Verfügbarkeit is specified as a percentage for a given period (for example, 99.9% per year). This implies an allowable downtime over that period (for 99.9% over one year, about 8.76 hours of unplanned downtime are permissible, assuming planned downtime is excluded). Organizations use Soll-Verfügbarkeit to plan maintenance windows, allocate redundancy, and negotiate service levels with customers or internal departments.

Common contexts include IT services, manufacturing facilities, and critical infrastructure, where high availability is essential. Related concepts include Ist-Verfügbarkeit, uptime, downtime, MTBF, MTTR, and service level agreements.