Maximums: You can have a maximum of 1024 luns and 128 targets x cluster. Also, these luns are not meant to be used by other esxi hosts. They are meant to be used by other (non vSphere) environments.
Step 1: As you use the Web Client , select the cluster, go to Configure and iSCSI Targets. The iSCSI service is disabled by default. Click on Edit on the top right corner to enable it.
Step 2: Click on Edit and enable the Virtual SAN iSCSI service. Select the iSCSI network, the port to use (3260 is the default) and your authentication preferences (CHAP and Mutual CHAP are supported). Also, select the policy to use for the object (FTT=0 or something else if you desire).
Step 3: Click on the Green Plus Sign to add your first iSCSI target. Notice you don't have any once iSCSI is enabled.
Step 4: Select the lun ID (0 is the default) and the size of the lun (10gbs in this case).
Step 5: Get additional information and master the esxcli vsan iscsi namespace.
Step 6: Test your configuration. In this case, a Windows 7 pc was used to connect to the iscsi server and format the iscsi lun. Click on Start, type iscsi and select iscsi initiator. Enable the service.
Step 7: Go back to the Web Client and find out who is the owner of the iscsi lun/object. In this case, it was 10.1.1.11 (upper right corner)
Step 8: Input that ip address in the Targets column and connect.
Step 9: In the Windows pc, click on Start and type disk management. Select Create and Format Hard Disk Partitions. You should see a second drive that needs to be initialized.
Step 10: Select the new 10gb drive and format it.
Final Note: You can also configure iSCSI Initiator Groups to define which initiators can access the targets. To do so, click on the green plus sign to add an initiator group. Before doing this, go to the Windows pc, click on the configuration tab and document the initiator name.