Description of problem:
Chapter 2.3. Storage Domain Types of The Technical Reference states that "Additionally, it is required that the data center and data storage domain use the same protocol (for example, both must be iSCSI based)."

This limitation used to be correct, but is no longer relevant since RHEVM 3.4. It should be removed from the 4.0 documentation, and possibly from the published documentation for previous versions too, up to the documentation stakeholders.