The number of paths made available for the iSCSI initiator will depend upon the type of iSCSI storage array.

With single portal arrays, the storage array exposes a single portal to be discovered by the source (initiator). Hence, the number of paths to such an array will depend on the number of VMkernel interfaces associated with the iSCSI initiator. The process of associating VMkernel interfaces with an iSCSI initiator is called port binding. We will learn more about port binding in the Configuring iSCSI multipathing using port binding section of this chapter. Arrays such as the HP's HPE StoreVirtual and Dell EqualLogic are examples of single portal arrays.

With multi-portal arrays, the storage array exposes multiple portals to be discovered by the iSCSI initiator. Therefore, the number of paths to the array will not only depend on the number of VMkernel ports bound to the iSCSI initiator but also the number of portals exposed. For instance, if two VMkernel ports are bound to the iSCSI initiator discovering four target portals, then the number of paths to the iSCSI target is eight.

With multi-target arrays, the storage array can have more than one iSCSI targets, with one or more portals associated with them.

The formula for calculating the number of paths possible is dependent on the number of sources (VMkernel port) and target portals and not the number of targets:

Here, the source portal is nothing but the VMkernel interfaces bound to the iSCSI initiator.

When you view the multipathing information for single/multi-portal arrays from the vCenter GUI, every discovery portal will be listed as a target. These targets will have the same IQN, but different portal IP addresses associated with them. However, for multi-target arrays, you will see targets with different IQNs as well.