To access iSCSI targets, your ESXi host uses iSCSI initiators.
The initiator is a software or hardware installed on your ESXi host. The iSCSI initiator originates communication between your host and an external iSCSI storage system and sends data to the storage system.
In the ESXi environment, iSCSI adapters configured on your host play the role of initiators. ESXi supports several types of iSCSI adapters.
For information on configuring and using iSCSI adapters, see Configuring iSCSI Adapters and Storage.
Software iSCSI Adapter
A software iSCSI adapter is a VMware code built into the VMkernel. Using the software iSCSI adapter, your host can connect to the iSCSI storage device through standard network adapters. The software iSCSI adapter handles iSCSI processing while communicating with the network adapter. With the software iSCSI adapter, you can use iSCSI technology without purchasing specialized hardware.
Hardware iSCSI Adapter
A hardware iSCSI adapter is a third-party adapter that offloads iSCSI and network processing from your host. Hardware iSCSI adapters are divided into categories.
Dependent Hardware iSCSI Adapter
Depends on VMware networking, and iSCSI configuration and management interfaces provided by VMware.
This type of adapter can be a card that presents a standard network adapter and iSCSI offload functionality for the same port. The iSCSI offload functionality depends on the host's network configuration to obtain the IP, MAC, and other parameters used for iSCSI sessions. An example of a dependent adapter is the iSCSI licensed Broadcom 5709 NIC.
Independent Hardware iSCSI Adapter
Implements its own networking and iSCSI configuration and management interfaces.
Typically, an independent hardware iSCSI adapter is a card that either presents only iSCSI offload functionality or iSCSI offload functionality and standard NIC functionality. The iSCSI offload functionality has independent configuration management that assigns the IP, MAC, and other parameters used for the iSCSI sessions. An example of an independent adapter is the QLogic QLA4052 adapter.
Hardware iSCSI adapters might need to be licensed. Otherwise, they might not appear in the client or vSphere CLI. Contact your vendor for licensing information.