vSphere Distributed Resource Scheduler (DRS) explained

VMware vSphere Distributed Resource Scheduler (DRS) is a feature that enables a virtual environment to automatically balance itself across your ESX hosts in a cluster in an effort to eliminate resource contention. The goals of DRS are:

  • at startup, DRS attempts to place each VM on the host that is best suited to run that virtual machine.
  • while a VM is running, DRS seeks to provide that VM with the required hardware resources while minimizing the amount of contention for those resources in an effort to maintain balanced utilization levels.

If a DRS cluster becomes unbalanced, DRS can migrate VMs from overutilized ESXi hosts to underutilized hosts. DRS performs these migrations of VMs across hosts in the cluster without any downtime by using vMotion. You can determine whether DRS will just display migration recommendations or automatically perform the migration when the cluster becomes unbalanced by defining the automation level.

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