It seems only one host can connect to my iscsi storage when using iscsi port binding (multipath). When I don't use port bindings, both hosts can see the storage. ie right click iscsi initiator properties and remove port bindings. When I do put in the port bindings, the first host (Host A) can see the iscsi storage. When I add my port bindings to the second host I cannot see storage. If I remove all the port bindings across both hosts and do the port bindings to Host B first then I can see the storage and when I do Host A second I don't see storage. Basically only one host at a time can see iscsi storage if using port bindings and both hosts can see storage if no bindings used at all.
My Setup,
Two ESXi 5.1 hosts
Two vmkernels on designated iscsi vlan
ethernet port profile for iscsi with two physical ports assigned from each host
vethernet port profile for iscsi
All four vmkernel IPs are on the same subnet
MTU 9000 on ethernet pp and vmkernels
Hosts are behind a router which NATs the hosts. ISCSI storage is outside the router. So the hosts would be seen with the same IP by the iscsi storage but with a different port number. I don't know if they has any effect. But again, if hosts don't use port bindings the storage works fine.