The iSCSI multipath feature sets up multiple routes between a server and its storage devices for maintaining a constant connection and balancing the traffic load. The multipathing software handles all input and output requests and passes them through on the best possible path. Traffic from host servers is transported to shared storage using the iSCSI protocol that packages SCSI commands into iSCSI packets and transmits them on the Ethernet network.
iSCSI multipath provides path failover. In the event a path or any of its components fails, the server selects another available path. In addition to path failover, multipathing reduces or removes potential bottlenecks by distributing storage loads across multiple physical paths.
1. 
Uplink Pinning
Each VMkernel port created for iSCSI access is pinned to one physical NIC.
This overrides any NIC teaming policy or port bundling policy. All traffic from the VMkernel port uses only the pinned uplink to reach the upstream switch.
2. Storage Binding
Each VMkernel port is pinned to theVMware iSCSI host bus adapter (VMHBA) associated with the physical NIC to which the VMkernel port is pinned.
The ESX or ESXi host creates the following VMHBAs for the physical NICs.
–In Software iSCSI, only one VMHBA is created for all physical NICs.
–In Hardware iSCSI, one VMHBA is created for each physical NIC that supports iSCSI offload in hardware.