External storage can be used with VMware Cloud Foundation on VxRail (NFS/iSCSI/FC) to compliment primary vSAN storage for workload domain clusters. This is known as supplemental storage.
External secondary storage is primarily used for:
Supporting external storage in VMware Cloud Foundation for VxRail is comparable to the experience of administrators using standard vSphere clusters who want to attach secondary datastores to those clusters. For VMware Cloud Foundation, this mounting process is performed manually using standard vCenter operations procedures. The platform does not take ownership of the life cycle management, storage provisioning, or network (IP or FC) configuration or zoning for the external storage systems. Instead, administrators use the native storage system and network management tools for those tasks.