vSphere vMotion explained
vSphere vMotion is a vSphere migration mechanism that moves a powered-on virtual machine from one ESXi host to another, with no service disruption or downtime. The entire state of a virtual machine that is being migrated is moved from one ESXi host to another, including the memory content and all the information that define the virtual machine, such as BIOS, devices, MAC addresses, etc.
Because vMotion is performed as a live migration of a VM from one ESXi host to another ESXi host without service interruption, there are no dropped network connections and applications continue to run uninterrupted. In fact, end users are not even aware that the VM has been migrated between two physical ESXi hosts.
vSphere vMotion is especially useful during the hardware maintenance. If an physical ESXi host needs to be powered off for hardware maintenance during production hours, vMotion can be used to migrate all active VMs to another physical host without service downtime. After the hardware maintenance has been performed, VMs can be migrated back to the old host.