Which technology does vSphere use for enabling the migration of running virtual machines without downtime?

vSphere leverages vMotion to enable the live migration of running virtual machines (VMs) without any downtime. This technology allows an active VM to be moved from one physical host to another while remaining powered on and operational. During the migration, vMotion utilizes a combination of techniques, including memory replication and state synchronization, to ensure that the VM continues to process incoming requests seamlessly.

This capability is crucial in maintaining availability, performing hardware maintenance, balancing loads, and optimizing resource utilization in a virtualized environment. The transparent nature of this process ensures that end-users experience no interruption in service, making vMotion a vital feature for enterprises that require high availability for their applications.

Other options like Storage DRS, VM snapshots, and Resource Allocation serve different purposes—such as optimizing storage performance and space, creating point-in-time copies of VMs, and managing resource distribution—but they do not facilitate the live migration of VMs like vMotion does.