iSCSI is a protocol designed to transmit SCSI commands over the network. Like regular SCSI devices, the protocol is designed to interact with datastores on a block level. VMware treats iSCSI devices like any other block device presented to the vSphere hosts.
There are two main ways to interact with an iSCSI storage device: hardware and software iSCSI adapters. Here's a brief description of each:
Hardware iSCSI adapters are add-on cards added to the host or embedded in the network adapter of the host. iSCSI adapters present the host with an HBA that can be used to write data to attached disks. Hardware iSCSI adapters have the advantage of higher performance and lower latency over software iSCSI adapters but may require special drivers or out of band or command line configuration.
A software iSCSI adapter is a software stack that interacts with iSCSI storage datastores over the NICs attached to the vSphere host. Software iSCSI adapters come standard with the VMware vSphere kernel and can...