Here they are artilces that explains, on old ESX 5, how to configure iSCSI Multipathing.
Mainly used with single SAN and dual controller to manage single controller fault (or Fiber channel problems).
iSCSI Multipathing
"When transferring data between the host server and storage, the SAN uses a technique known as multipathing. With multipathing, your ESXi host can have more than one physical path to a LUN on a storage system.
Generally, a single path from a host to a LUN consists of an iSCSI adapter or NIC, switch ports, connecting cables, and the storage controller port. If any component of the path fails, the host selects another available path for I/O. The process of detecting a failed path and switching to another is called path failover.
For more information on multipathing, see Understanding Multipathing and Failover."
I am adding it to blog toolbox.
How to Configure iSCSI Multipathing (MPIO) in VMware vSphere 5 using ESXCLI
http://www.cosonok.com/2012/01/how-to-configure-iscsi-multipathing.html
How to Configure iSCSI Multipathing (MPIO) in VMware vSphere 5 using ESXCLI (UPDATE)
http://www.cosonok.com/2012/06/how-to-configure-iscsi-multipathing.html
indeed here it is official Vmware documentation:
https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/vmware-multipathing-configuration-software-iscsi-port-binding-white-paper.pdf
and relative concept explaination:
https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.storage.doc/GUID-AE0C1165-521D-4E65-9921-35F9F6EB39AA.html