A discovery session is part of the iSCSI protocol. The discovery session returns the set of targets that you can access on an iSCSI storage system.
ESXi systems support dynamic and static discovery.
For either case, you set up target discovery addresses so that the initiator can determine which storage resource on the network is available for access. You can do this setup with dynamic discovery or static discovery. With dynamic discovery, all targets associated with an IP address or host name and the iSCSI name are discovered. With static discovery, you must specify the IP address or host name and the iSCSI name of the target you want to access. The iSCSI HBA must be in the same VLAN as both ports of the iSCSI array.