Which of the following is NOT a metric for assessing system availability?

System availability metrics are critical for evaluating how effectively an information system operates without interruptions. Metrics such as Agreed Service Time (AST), Minimal Downtime (DT), and Maximum Tolerable Downtime (MTD) specifically focus on time-related aspects of system availability. AST indicates the time agreement between service providers and users for when services will be available, DT refers to the least downtime considered acceptable for operations, and MTD defines the maximum period a system can be down before significant impact occurs.

In contrast, the cost of service outages does not directly measure system availability. While this metric assesses the financial impact of downtime on a business, it does not quantify the availability or uptime of the system itself. Therefore, it is not considered a direct metric for assessing system availability, making it the correct option in this context.