Which of the following concepts allows an organization to group large numbers of servers together in order to deliver a common service?

Server clustering links multiple physical or virtual servers so they share workloads and provide failover capability, presenting a single service endpoint to clients. This allows the organization to scale horizontally and ensures that the failure of one server does not interrupt the service. Clustering is widely used for database servers, web servers, and application servers requiring high uptime.

RAID (Redundant Array of Independent Disks) provides disk-level redundancy and fault tolerance for storage, but it groups drives, not servers, and does not deliver a common service across machines.

Backup redundancy refers to maintaining copies of data to enable restoration after failure or loss, which is a data protection strategy rather than a server grouping mechanism.

A cold site is a disaster recovery facility that has power and connectivity but no pre-installed equipment, used for recovery purposes rather than for grouping servers to deliver a service.