Which two factors define a layered security approach in data centre design?

A layered security approach, also known as "defense-in-depth," is defined by the creation of multiple, sequential barriers that an intruder must overcome. This strategy is characterized by establishing several independent protection zones (e.g., site perimeter, building exterior, data hall, server rack). Access between these zones is strictly managed through controlled access points, such as gates or doors equipped with authentication mechanisms. The failure of one layer does not compromise the entire facility.

B: A single-entry system is a security tactic within a layer, not a defining factor of the multi-layered approach itself.

C: Effective security requires a mix of passive (monitoring) and active (deterrent, response) measures, not just passive surveillance.

D: Open visitor access is a severe security vulnerability that directly contradicts the principle of controlled access in a layered model.

1. Schneider Electric, "White Paper 141: Physical Security in the Data Center," Rev 1, 2014, p. 3. Describes the layered approach as "concentric circles of protection around the assets," with each circle representing a zone with controlled access.

2. Mori, P., Martinelli, F., & Raponi, P. G. (2012). Design of a physical security system for a data center. 2012 IEEE 11th International Conference on Trust, Security and Privacy in Computing and Communications, 1138-1145. https://doi.org/10.1109/TrustCom.2012.144. Section III.A discusses the layered security model based on distinct security zones.