VMware vSphere Clustering Service (vCLS) was introduced in the vSphere 7 Update 1 release with the idea of creating a decoupled and distributed control plane for clustering services in vSphere.

But with VMware vSphere 8.0.3, the vSphere Clustering Service (vCLS) will be “migrated” with a new Embedded vSphere Cluster Service model. The entire vSphere Cluster Service (vCLS) is rearchitected to use fewer resources, remove storage footprint, and eliminate issues associated with vCLS deployment.

But with VCF and VVF 9.0 there is a news… if you look at the VMware vSphere Clustering Service (vCLS) settings you will see this warning:

VMware vCenter 9.0 deprecates vCLS, and the service will be removed in a future vCenter release. 

Note that vCenter 9.0 also deprecates the requirement for vCLS to be active on clusters and recommends vCLS to be switched to retreat mode to avoid the redundant usage of resources. Deactivating vCLS does not impact the operation of vSphere DRS and  vSphere HA services.

To swith to retreat mode, see KB 316514.

It’s not clear why, but maybe because in version 9 the ESXi hosts in a cluster contain a distributed key-value store of cluster state:

The distributed key-value store is the source of truth for the state of the cluster. If vCenter is restored from a backup, it will reconcile the cluster state and configuration with the distributed key-value store. In vSphere 9, host-cluster membership is reconciled with additional configuration and state planned for support in future releases.