You can create a VSAN at the domain group root or in a specific domain. You can also assign the VSAN to either fabric A or fabric B, or to both fabric A and B.
When you assign the VSAN to both fabrics, both of them must have different VSAN ID and FCoE VLAN ID.
https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/ucs-central/GUI-User- Guides/Storage-Mgmt/1-5/b_CiscoUCSCentral_Storage_Management_Guide_1-5/b_CiscoUCSCentral_Storage_Management_Guide_1-5_chapter_011.pdf

When a client wants to perform some type of action on a file on a particular machine, it uses RPC to make a call to the NFS server on that machine. The server accepts the request and performs the action required, then returns a result code and possibly data back to the client, depending on the request. The result code indicates if the action was successful. If it was, the client can assume that whatever it asked to be done was completed. For example, in the case of writing data, the client can assume the data has been successfully written to long-term storage.
NFS can operate over any transport mechanism that has a valid RPC implementation at the session layer.

Explanation
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