In order to configure multipathing for an iSCSI storage device we can configure software iSCSI port binding on an ESXi Host in order to load-balance between paths when all paths are present and to handle failures of a path at any point between the server and the storage. Without port binding, all iSCSI LUNs will be detected using a single path per target. By default, ESX will use only one vmknic as an egress port to connect to each target, and you will be unable to use path failover or to load balance I/O between different paths to the iSCSI LUNs
To enable vmknic-based software iSCSI multipathing, we must perform the following from the vSphere Web Client:
1) Select the ESXi host system we wish to configure the Software iSCSI port binding.
2) Select Manage > Networking.
3) Select Add Host Networking and VMkernel Network Adapter.
4) Create a new Standard Switch (vSS).
5) Assign two physical network adapters, in this example vmnic1 and vmnic2.
6) Specify a network label, in the first instance I will name this vmk-iscsi-1.
7) Assign an IPv4 address to the the VMkernel Network Adapter.
8) Select Finish to complete the configuration.
Now, I will repeat Steps 3-8, but I will use the existing Standard Switch (vSS) I previously created assign the network label vmk-iscsi-2 and configure a unique IPv4 address. Once you have created two VMkernel Network Adapters on the Standard Switch (vSS) we will need to configure the failover order of each one to assign only a single active unique physical network adapter.
1) Highlight the VMkernal Network Adapter vmk-iscsi-1 and select Edit.
2) Select Teaming and Failover, enable the Override option and specify vmnic1 as the active adapter and vmnic2 as the unused adapter.
Again, repeat the above steps but for vmk-iscsi-2 select the active adpater as vmnic2 and the vmnic1 as the unused adapter. Finally, we need to configure the network configuration of our Software iSCSI adapter to bind to port VMkernel Network Adapters created in the above steps.
1) Select Manage > Storage > Storage Adapters.
2) Highlight the Software iSCSI Adapter and select Network Port Binding.
3) Add both vmk-iscsi-1 and vmk-iscsi2 and rescan the adapter to apply the configuration.