Scenario: You are tasked with scalability testing for a cloud-based storage service. During the test, you observe that adding more virtual machines to the cluster does not significantly improve performance. What scalability issue might you be facing?

Horizontal Scalability refers to the ability to increase capacity by adding more instances or nodes to a distributed system. If adding more virtual machines to the cluster doesn't notably enhance performance, it indicates a horizontal scalability issue. This could imply that the system architecture lacks proper distribution or that there are bottlenecks elsewhere in the infrastructure preventing efficient utilization of additional resources. Addressing such issues may involve optimizing data distribution, improving communication between nodes, or reconfiguring load balancing mechanisms.