VMware DRS
A VMware DRS cluster is a collection of ESXi hosts and associated virtual machines with shared resources and a shared management interface. To obtain the benefits of cluster-level resource scheduling you create a DRS cluster.
When you add a host to a DRS cluster, the host’s resources become part of the cluster’s resources. In addition to aggregation of resources, a DRS cluster supports cluster-wide resource pools and enforces cluster-level resource allocation policies. The following cluster-level resource management capabilities are available.
- Load Balancing. The vCenter Server monitors distribution and use of CPU and memory resources for all hosts and virtual machines in the cluster. DRS compares these metrics to an ideal resource utilization given the attributes of the cluster’s resource pools and virtual machines, the current demand, and the DRS Score, which measures the execution efficiency of the virtual machine. DRS then performs (or recommends) virtual machine migrations. When you first power on a virtual machine in the cluster, DRS attempts to maintain proper load balancing either by placing the virtual machine on an appropriate host or by recommending one.
- Power Management. When the VMware DPM (Distributed Power Management) feature is enabled, DRS compares cluster- and host-level capacity to the demands of the cluster’s virtual machines, including recent historical demand. DPM places (or recommends placing) hosts in standby power mode if sufficient excess capacity is found. DPM powers on (or recommends powering on) hosts if capacity is needed. Depending on the resulting host power state recommendations, virtual machines might need to be migrated to and from the hosts.
- Virtual Machine Placement. You can control the placement of virtual machines on hosts within a cluster, by assigning DRS affinity or antiaffinity rules.