The most useful information to determine mitigating controls when a core data center went offline abruptly for several hours affecting many transactions across multiple locations is the root cause analysis. Root cause analysis is a technique that identifies the underlying factors or reasons that caused the problem or incident.
Root cause analysis can help to understand the nature, scope, and impact of the problem or incident, and to prevent or reduce the recurrence or severity of the problem or incident in the future. Root cause analysis can also help to identify and prioritize the appropriate mitigating controls that address the root causes of the problem or incident. The other options are not as useful as root cause analysis, as they are related to the investigation, evaluation, or measurement of the problem or incident, not the resolution or prevention of the problem or incident. References = Risk and Information Systems Control Study Manual, Chapter 4: Risk and Control Monitoring and Reporting, Section 4.4: Key Control Indicators, page 211.