What function does vMotion perform in VMware vSphere?

vMotion is a critical feature in VMware vSphere that allows for the seamless migration of running virtual machines from one ESXi host to another without any downtime. This capability is essential for various operational tasks, including load balancing, hardware maintenance, and optimizing resource utilization.

When a virtual machine is migrated using vMotion, the memory and the state of the virtual machine are transferred over the network to the destination host while the virtual machine continues to operate. This ensures that users experience no noticeable interruption, making it a powerful feature for maintaining high availability and reliability in virtualized environments.

This function contrasts with the other options, which touch on different aspects of VMware technology. For instance, migrating virtual machines between physical storage devices pertains to storage vMotion, which is not the same as vMotion and specifically deals with storage management rather than host management. The compression of data for storage efficiency doesn't pertain to vMotion but rather involves other storage technologies. Lastly, balancing storage allocations across datastores is managed through different means, such as Storage DRS, which focuses on optimizing storage but does not involve the movement of running VMs as vMotion does.