The failure rate goal that is acceptable must be set separately for each level of problem severity - from critical to low.
A customer may be willing to tolerate tens of low-severity issues per day but not more than one critical problem in a year.
System availability consists of proactive methods for maximizing service uptime, for minimizing the downtime, and for minimizing the time needed to recover from an outage. Downtime is measured in terms of MTTR.
Gathering an operational profile from the customer facilitates the creation of a customer environment. An operational profile describes the ways the system is to be used. One can uncover several deficiencies in the system while tuning the parameters of the system; parameter tuning will improve system availability level.
Customers must be willing to share the operational profile of their computing environment to improve the target availability level, which may be proprietary information.
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