Uneven distribution of virtual machines across homogeneous cluster in VMware vSphere DRS

Products

• VMware vSphere ESXi

Issue/Introduction

• VMware vSphere Distributed Resource Scheduler (DRS) distributes workloads unevenly across a homogeneous cluster where hosts have matching CPU and memory specifications.
• Virtual machines (VMs) are not experiencing resource contention.
• DRS Automation Level is configured to "Fully Automated."
• No active alarms, VM-Host affinity rules, or placement policies are configured that would explain the behavior.

Environment

VMware vSphere 8.x

Cause

In vSphere 8.x, the DRS engine focuses on "VM Happiness" (Resource Satisfaction). If VMs receive the resources required to perform optimally on their current host, DRS does not migrate them solely to balance the VM count evenly across the cluster.

Resolution

To prioritize an even distribution of VMs across hosts in the cluster, enable the VM Distribution feature:

1. Log in to the vSphere Client and select the required Cluster.
2. Navigate to Configure and select Edit under DRS settings.
3. Expand the Additional Options menu.
4. Select the VM Distribution checkbox.
5. Click OK to save changes.

Note: Enabling this feature changes default DRS behavior. DRS will prefer a host with a lower number of VMs when choosing a placement. For a migration to occur, a VM must have a "goodness" metric low enough to justify the relocation cost.

Additional Information

Performance Best Practices for VMware vSphere 8.0 Update 3