From a risk management standpoint, the best approach for implementing a large and complex data center infrastructure is a deployment plan based on sequenced phases. ISACA guidance repeatedly supports phased implementation for complex, high-risk changes because it allows the organization to manage dependencies, reduce disruption, validate results incrementally, and maintain operational continuity while lessons from earlier phases can inform later ones.

Option D is correct because phased deployment reduces concentration of implementation risk. Instead of exposing the organization to a single large-scale failure point, phased rollout allows testing, adjustment, monitoring, and controlled transition. ISACA material discussing complex implementations emphasizes structured, phased approaches to handle technical debt, compatibility issues, and continuity concerns.

Option A is incorrect because a big bang deployment concentrates risk, even if a proof of concept was successful. A proof of concept demonstrates feasibility in limited conditions, but it does not eliminate the operational risks of a full-scale one-time cutover in a complex environment. For large infrastructure changes, CISA logic generally prefers phased approaches over big bang implementations.

Option B is useful, but simulation alone is not the best answer. Simulation can support planning and testing, yet it does not by itself provide the controlled risk reduction that phased deployment offers during actual implementation. In CISA questions, the best risk-management choice is usually the one that combines control and gradual exposure reduction, which is phased rollout.

Option C is incorrect because “prototyping and a one-phase deployment” still culminates in a single-phase rollout, which is riskier than sequenced deployment. A prototype can improve design understanding, but it does not replace the value of incremental implementation in a complex production environment.

Therefore, D is the best answer because a sequenced, phased deployment is the most effective risk-management approach for large and complex infrastructure implementations.

References (Official ISACA):

ISACA, Passwordless Authentication: Risk, Reward, and Readiness — supports a carefully crafted phased implementation to manage complexity and maintain continuity.

ISACA Journal, Working Toward a White Box Approach — highlights the risks created by complexity in large IT initiatives.

ISACA Journal, Essential Frameworks and Methodologies to Maximize the Value of IT — supports structured project and program management sequencing.

ISACA Journal, A Strategic Risk-Based Approach to Systems Security Engineering — supports using a risk-based approach for complex systems change.