You can override default vCLS VM datastore placement.

vSphere Cluster Services (vCLS) VM datastore location is chosen by a default datastore selection logic. To override the default vCLS VM datastore placement for a cluster, you can specify a set of allowed datastores by browsing to the cluster and clicking ADD under Configure > vSphere Cluster Service > Datastores. Some datastores cannot be selected for vCLS because they are blocked by solutions like SRM or vSAN maintenance mode where vCLS cannot be configured. Users cannot add or remove Solution blocked datastores for vCLS VMs.