Service s need to be recovered as quickly as possible when they become unavailable to user s. Mean Time to Restore Service (MTRS) for a service, system or component is the time taken on average to restore its full functionality. This includes not only any physical repair or replacement, but also all the other factors that contribute towards full functionality. It is possible to estimate the MTRS of a service only when there is sufficient data available about the supporting configuration of service asset s. MTRS is a measure that depends on several factors including the following:
Adjustments to the above factors in isolation or combination increase maintainability. Analysis of the way MTRS responds to each factor is useful for improving the design of services and performance in operation. Reducing any of the following factors can reduce MTRS (Figure 7.19):
Figure 7.19 Improvement opportunities within incident lifecycle
It is normal to measure time strictly in real terms of seconds, minutes, hours and days. The periodicity of business activity varies between customers and contract s. In situations where the rate of loss to the business is linear with time, it is useful to measure the time factors indirectly in terms such as cycles, miles, transaction s and trades to sense the true impact on business.
Toolbox Tip
Methods and principles of Design of Experiments (DOE), Six Sigma and system s dynamics modelling methods are useful in developing decision model s for maintainability and reliability.
Redundancy
Redundancy is a means of increasing reliability and maintainability of systems. High- availability systems typically have some level of redundancy built in. There are four primary types of redundancy useful selectively or in combination: active, passive, diverse and heterogeneous (Figure 7.20).
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