Migrating vCLS VM to another datastore.
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Migrating vCLS VM to another datastore.

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Article ID: 396571

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Updated On: 05-19-2025

Products

VMware vCenter Server

Issue/Introduction

The vSphere Cluster Service VM (vCLS VM) is deployed from an OVA with a minimal installation profile based on PhotonOS. vCLS VMs are responsible for managing the resources, power state, and availability of services within the cluster. They play a crucial role in maintaining the health and availability of vSphere Cluster Services, which include features such as vSphere DRS (Distributed Resource Scheduler) and vSphere HA (High Availability). Any disruption to the power state or resources of these VMs can negatively impact the health of the vSphere Cluster Service, potentially causing vSphere DRS to cease operation within the cluster.

Best Practices for vCLS VM Management:

  • Avoid Manual Migration via vMotion:
    It is strongly not recommended to migrate vCLS VMs to another datastore via vMotion, as vCLS VMs are not standard virtual machines. They are critical to the proper functioning of cluster services and should not be treated like normal VMs when it comes to migration.

  • Automatic Placement by vCenter:
    The placement of vCLS VMs is managed automatically by the vCenter Server. Users are not provided with the option to manually select the target datastore for vCLS VM placement. vCenter uses an internal logic to select an appropriate shared datastore for the cluster if one is available and has sufficient capacity to host these VMs. This ensures that vCLS VMs are placed on datastores that are suitable for their operation.

vSphere Cluster Services in vSphere 7.0 Update 1:

Introduced in vSphere 7.0 Update 1, vSphere Cluster Services (vCLS) ensure that critical cluster services, such as vSphere DRS and vSphere HA, remain operational and available to manage workloads within the cluster. With this release, VMware provides a framework to enable these services to run independently of the vCenter Server instance. While vCenter Server is still required for the configuration and management of cluster services, vCLS VMs ensure the continued health of the cluster services even in the event of vCenter Server unavailability.

Key Points:

  • Health of vCLS VMs:
    The health of vSphere DRS and other cluster services depends on the health of the vCLS VMs. If these VMs are not properly maintained or their state is altered, it could lead to the malfunctioning of DRS, impacting resource management in the cluster.

  • Note on vSphere DRS in vSphere 7.0 Update 1:
    Starting with vSphere 7.0 Update 1, vSphere DRS depends on the health of vCLS to operate correctly. Therefore, ensuring the stability and availability of vCLS VMs is critical for DRS functionality.

vCLS in vSphere 8.0 U3 - Embedded vCLS:

In vSphere 8.0 U3, VMware has introduced a new version of vCLS known as Embedded vCLS. This version of vCLS is used when both vCenter and ESXi are upgraded to 8.0 U3. It is designed to be embedded directly within the vSphere environment to provide more efficient operation. The previous version of vCLS, known as External vCLS, was used prior to vSphere 8.0 U3.

Conclusion:

The vCLS VMs are an integral part of the cluster management framework in vSphere and play a key role in maintaining the availability of cluster services such as DRS and HA. Users should follow the recommended guidelines for managing these VMs to ensure smooth cluster operations and prevent issues with resource management and HA functionality.

Environment

vSphere 7.0 Update 1

vSphere 7.0 Update 2

vSphere 7.0 Update 3

vSphere 8.0 Update 1

vSphere 8.0 Update 2

Cause

Manual migration of vCLS VMs can result in the following error:

"vSphere DRS functionality was impacted due to unhealthy state of vSphere Cluster Services caused by the unavailability of vSphere Cluster Service VMs. vSphere Cluster Service VMs are required to maintain the health of vSphere DRS."

Resolution

Resolution:

To move the vCLS VMs to another datastore, follow the recommended procedure below:

  1. Enable "retreat mode" on the cluster to allow deletion of vCLS VMs.

  2. Disable DRS (Distributed Resource Scheduler) on the cluster.

  3. Add the datastore to the list of allowed datastores for vCLS VMs.

  4. Disable retreat mode to allow automatic deployment of vCLS VMs.

  5. Re-enable DRS on the cluster.

Note: Disabling DRS can result in the loss of the resource pool configuration. It is strongly recommended to backup the resource pool before disabling DRS.

Additional Information