Anti-affinity is the concept of ensuring that certain virtual machines or workloads do not run on the same physical host. This can improve the availability and performance of the system, as well as prevent a single point of failure. In this scenario, the systems administrator needs to ensure the database nodes do not exist on the same physical host, so anti-affinity would best meet this requirement. Oversubscription is the concept of allocating more resources to virtual machines than the physical host actually has, which can improve the utilization and efficiency of the system, but it does not guarantee the separation of the database nodes. A firewall is a device or software that controls the network traffic between different zones or segments, which can improve the security and isolation of the system, but it does not affect the placement of the database nodes. A separate cluster is a group of hosts that share common resources and policies, which can improve the scalability and manageability of the system, but it does not ensure the database nodes do not exist on the same physical host within the cluster. References: CompTIA Cloud+ CV0-003 Certification Study Guide, Chapter 1, Cloud Architecture and Design, page 131.