vSphere iSCSi not suport VM Cluster?

I'm building a virtual machine cluster using vSphere 5.1.

I'm finding solution for data storage.

I want iSCSi but when I see information on vsphere documentation I see with iSCSi vSphere don't supports "VM Cluster" but supports HA and DRS. I known HA only enable when create a "Cluster (Host cluster)".

(VMware vSphere 5.1)

I don't know exactly "VM Cluster" is what.

Please help me explain different of "VM Cluster" and "Host Cluster".

Thanks a lot!