What happens when you click the "RUN DRS NOW" button in vSphere?

When the "RUN DRS NOW" button is clicked in vSphere, it triggers an immediate evaluation of the cluster managed by Distributed Resource Scheduler (DRS). During this evaluation, DRS identifies the best allocation of resources based on the current state of the virtual machines and hosts.

The key aspect of this action is that only the highest priority recommendations are applied at that moment. DRS analyzes various factors such as resource load, VM placement, and affinity rules, and then prioritizes the recommendations to ensure that the most critical adjustments to resource allocation are made first. This behavior helps maintain overall cluster performance and efficiency by addressing the most pressing needs of workloads before considering less urgent adjustments.

While it would be helpful to apply all recommendations at once, the focus on applying only the highest priority ones is designed to optimize resource distribution effectively and minimize disruption to running workloads. This makes the management of resources within the cluster more efficient and responsive to immediate needs.