A cluster is a set of physical hosts that are treated as a resource pool for a set of virtual machines. Hosts in a cluster share the same network infrastructure and the same storage. They are a migration domain within which virtual machines can be moved from host to host.
Using the test mapped to this layer, you can quickly understand how much CPU/memory/storage resources are available with each cluster managed by an RHEV manager, and assess how well every cluster utilizes the available resources. In the process, the test points you to those clusters that may run the risk of a resource contention in the future.
Figure 1 : The test mapped to the Virtual Machine Clusters layer