When you attempt to power on a single virtual machine or a group of virtual machines in a DRS-enabled cluster, vCenter Server performs admission control. It checks that there are enough resources in the cluster to support the virtual machine(s).

If the cluster does not have sufficient resources to power on a single virtual machine, or any of the virtual machines in a group power-on attempt, a message appears. Otherwise, for each virtual machine, DRS generates a recommendation of a host on which to run the virtual machine and takes one of the following actions

  • Automatically executes the placement recommendation.
  • Displays the placement recommendation, which the user can then choose to accept or override.
    Note: No initial placement recommendations are given for virtual machines on standalone hosts or in non-DRS clusters. When powered on, they are placed on the host where they currently reside.
  • DRS considers network bandwidth. By calculating host network saturation, DRS is able to make better placement decisions. This can help avoid performance degradation of virtual machines with a more comprehensive understanding of the environment.