ESXi 5.5 and Compellent iSCSI best practices

We have ESXi 5.5 and Compellent SC8000. 

Both controllers have IP-address on different subnet 

I have two VMkernel ports on different subnets. Both on a different vSwitch.

Dell states port bindng should not be used. So both VMkernel ports should not be added to the Networking tab of the iSCSI software adapter. 

However this configuration does not work. HBA Rescan takes ages and datastores are not connected. 

What does work is this: 

1 vSwitch, 2 Vmkernels in 2 IP-subnets. Add those two vmkernels to the Networking tab of the iSCSI adapter.

What is the best practice?