Edwin -
The connections highlighted in the diagram are FC ISLs between the switches.
All four controllers have connectivity to all of the disk shelves.
I don't see the FC SAS bridges that would be there included in the diagram ?
NVRAM is also mirrored 4X in a Cluster Mode Metrocluster implementation.
It's a bit complex.
There's a 2 day MCCIW Metrocluster Cluster Mode Installation Workshop class we teach where we cover this all in detail.
As for your second question...
There's things we can do with a SAN migration appliance.
NAS workload migration is mostly host based.
There are various non-disruptive methods based on the application.
(VMware, Oracle, other)
The questions you ask aren't easy ones to answer with a short post to the community...
I hope this response has been helpful to you.
At your service,
Eugene E. Kashpureff, Sr.
Independent NetApp Consultant http://www.linkedin.com/in/eugenekashpureff
Senior NetApp Instructor, IT Learning Solutions http://sg.itls.asia/netapp
(P.S. I appreciate 'kudos' on any helpful posts.)