How does surviving partner get all LUN/Volumes information of DOWN filer , where this information is saved and how it is communicated to surviving partner ?

The information from the down filer is saved in the mailbox section of the NVLOG, which is part of the NVRAM. The mailboxes in the cluster is kept in the root volume of both running filers. If one filer fails, and surviving filer to “take over” the loop B side of the failed controller, and inadvertently assume control of the root volume of the failed controller. Since the surviving controller runs 2 halves of the NVRAM (one is its own, and one the failed controller), the entire architecture continues to run.

How is the HOST connectivity (ethernet) maintained incase of cluster failover ?
Guys, You have to ensure several components are installed to ensure network connectivity
 
a) Dual NIC ports, each going to different Ethernet switches.
b) NIC team is a must
c) Multi pathing for iSCSI is a must
d) Switches should be configured with some trunking mechanism – EtherChannel or Link Aggregation
e) At the filer end, dual network connectivity to network switches with trunking set up
f)  A much better architecture is to have quad network connectivity – ie. 2 ports from the host end and 4 ports from the filer end, OR 4 host ports and 4 filer network ports