vSphere Distributed Resource Scheduler (DRS) dynamically balances computing capacity across a collection of hardware resources aggregated into logical resource pools based on CPU and memory load status. vSphere DRS continuously monitors utilization across resource pools, or the root cluster resource pool, to intelligently allocate available resources among virtual machines based on a predefined set of rules that reflect business or application requirements. These vSphere vMotion migrations of virtual machines can be performed automatically or manually based on the defined parameters.

 

An additional benefit of DRS is realized when there is an operational requirement to place a host in maintenance mode. For instance, when servicing is required or to install additional memory on a host, all virtual machines that are running on the targeted host will be automatically migrated to other hosts within the cluster (assuming the DRS policies are configured appropriately to allow automatic migration). This provides a significant additional benefit gained from the vSphere HA admission control policy reserving spare capacity for both planned and unplanned outages. This can prove invaluable when performing rolling hardware maintenance or orchestrated patching through vSphere Update Manager. These types of actions can be carried out without any need to disrupt tenant services and are completely transparent to the consumers, providing non-stop IT services, maintenance without downtime, and greatly improved availability.