When setting up your ESXi host for multipathing and failover, you can use multiple iSCSI HBAs or multiple NICs depending on the type of iSCSI adapters on your host.
For information on different types of iSCSI adapters, see iSCSI Initiators.
When you use multipathing, specific considerations apply.
ESXi does not support multipathing when you combine an independent hardware adapter with software iSCSI or dependent iSCSI adapters in the same host.
Multipathing between software and dependent adapters within the same host is supported.
On different hosts, you can mix both dependent and independent adapters.
The following illustration shows multipathing setups possible with different types of iSCSI initiators.
Failover with Hardware iSCSI
With hardware iSCSI, the host typically has two or more hardware iSCSI adapters available, from which the storage system can be reached using one or more switches. Alternatively, the setup might include one adapter and two storage processors so that the adapter can use a different path to reach the storage system.
On the Host-Based Path Failover illustration, Host1 has two hardware iSCSI adapters, HBA1 and HBA2, that provide two physical paths to the storage system. Multipathing plug-ins on your host, whether the VMkernel NMP or any third-party MPPs, have access to the paths by default and can monitor health of each physical path. If, for example, HBA1 or the link between HBA1 and the network fails, the multipathing plug-ins can switch the path over to HBA2.
Failover with Software iSCSI
With software iSCSI, as shown on Host 2 of the Host-Based Path Failover illustration, you can use multiple NICs that provide failover and load balancing capabilities for iSCSI connections between your host and storage systems.
For this setup, because multipathing plug-ins do not have direct access to physical NICs on your host, you first need to connect each physical NIC to a separate VMkernel port. You then associate all VMkernel ports with the software iSCSI initiator using a port binding technique. As a result, each VMkernel port connected to a separate NIC becomes a different path that the iSCSI storage stack and its storage-aware multipathing plug-ins can use.
For information on how to configure multipathing for software iSCSI, see Setting Up iSCSI Network.