The vSphere cluster summary overview provides insights on what is happening from a DRS perspective. It is calculated using an aggregation of all the happiness VM scores in the cluster. DRS will try to maximize the execution efficiency of each virtual machine in the cluster while ensuring fairness in resource allocation to all virtual machines. Next to VM DRS Score, DRS presents the Cluster DRS Score in the UI. The improved DRS is no longer thinking about the relative load between ESXi hosts in a cluster, the main focus is on the happiness of the workloads. Will the virtual machine be able to burst resource consumption on its current host and to what level? Are there other ESXi hosts in the cluster that have more headroom available? All these factors play an important role in the calculation of the VM DRS score. The reserve resource capacity, or headroom, that a current ESXi host has is also taken into account to determine the VM DRS score.

The performance drivers for the VM DRS score are contention based, using metrics like CPU %ready time, good CPU cache behavior, and memory swap.

Not only performance metrics are used, but capacity metrics are also incorporated in the algorithm. That is because there are many metrics that influence the VM DRS score. It does not necessarily mean that a virtual machine in the 80-100% bucket is doing way better than a virtual machine in the lower buckets. Obtaining a VM DRS score of 80-100% indicates that there is mild to no resource contention. The score values range from 0 to 100% and are divided into buckets 0-20%, 20-40%, and so on.

First, let me emphasize that the VM DRS Score is not a health score for the virtual machine! It is about the execution efficiency of a virtual machine. The new DRS logic quantifies virtual machine happiness by using the VM DRS score.

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