Which of the following best describes clusters in the context of databases?

Clusters in the context of databases refer to multiple servers working together to manage data stored on a shared storage system. This setup allows for increased availability, scalability, and redundancy, as it enables the databases on different servers to access the same storage resources effectively. In a clustered environment, workloads can be distributed across the servers, enhancing performance and providing fault tolerance. If one server goes down, another can take over, minimizing downtime and ensuring continuous service.

The other options do not accurately describe the concept of clusters. For instance, having a group of databases on a single server does not constitute a cluster since clustering involves multiple servers. Similarly, data encryption is unrelated to clusters and focuses more on securing data rather than how databases are organized across servers. Lastly, the notion of single server databases for quick access does not involve shared storage or the collaboration of multiple servers, which are key elements in clustering architecture. Thus, the correct answer embraces the fundamental characteristics of clusters in database management systems.