Which vSphere feature allows for the migration of VMs without downtime?

vSphere vMotion is the feature that enables the live migration of virtual machines (VMs) from one physical host to another without any downtime. This capability allows administrators to move running VMs seamlessly while they continue to operate and provide services to users without interruption. The underlying process involves transferring the active memory and execution state of the VM from one host to another, which is accomplished while the VM keeps running. This is particularly beneficial for load balancing and maintenance operations, as it allows for the optimization of resource utilization without impacting the availability of the application or service.

This functionality differentiates vMotion as a superior method for VM management, especially in dynamic environments where uptime is critical. By contrast, other options may involve some level of interruption or are focused on different aspects of VM management, such as data replication or disaster recovery rather than seamless migration.