The Clusters navigation item contains clusters of computers. In a cluster preview and dialog, you can access a list of all nodes that belong to this cluster.
Clusters can be created manually, but are usually imported by the Inventory of VMware vCenter data provider.
A storage device is a type of asset whose purpose is to hold data while other devices can access this data and use it for computing. In a storage device preview and dialog, you can see a list of all computer systems that use this storage device.
Currently storage devices can be created only manually and then connected to other systems.