Error: VMK_RESERVATION_CONFLICT when validating Windows Server Failover Cluster (WSFC) on vSAN

Products

• VMware vSAN
• VMware vSphere ESXi 8.0

Issue/Introduction

This article addresses the VMK_RESERVATION_CONFLICT error encountered during the Microsoft Cluster Validation Wizard on VMware vSAN. This usually occurs when using cloned virtual machines for cluster nodes.

Environment

• VMware vSphere 8.x
• VMware vSAN 8.x
• Windows Server 2025 / 2022

Cause

The virtual machines participating in the cluster were cloned from a template. Cloned VMs may retain duplicate internal identifiers or inconsistent SCSI-3 Persistent Reservation states that prevent the cluster service from successfully arbitrating disk access.

Resolution

1. Power off and delete the affected cloned VMs.
2. Deploy new virtual machines from a fresh ISO installation (fresh install).
3. Configure the VMs according to the guidelines in KB 313472.
4. Ensure SCSI bus sharing is set to Physical and disks are Eager Zeroed Thick.
5. Re-run the Cluster Validation Wizard.

Additional Information:

• Refer to Microsoft Windows Server Failover Clustering (WSFC) with shared disks on VMware vSphere 8.x: Guidelines for supported configurations (313472)
• To speak with a customer representative or a Support Engineer see Contact Support.