Nowadays iSCSI is becoming popular in the new generation Storage Area Networks. Unlike Fibre Channel SANs, IP SANs use the iSCSI protocol over standard IP networks for host-to-storage communications. iSCSI is also becoming an increasingly popular mechanism to bridge disparate SAN islands and fabrics into a single large fabric. These advantages allow companies to leverage their existing investment in IP technologies to grow their Storage networks. In an IP SAN, hosts communicate with Storage Arrays using Serial SCSI-3 over IP. Gigabit Ethernet (GigE) is a commonly used medium for connectivity. This eliminates the need for a Fibre Channel HBA on the host. Modern server-class hosts typically ship with two network ports (NICs) in their factory configuration, with at least one port being GigE-capable. So no extra hardware may be needed on the host for iSCSI connectivity.
A network entity is a device (a client, server or gateway) that is connected to an IP network. It contains one or more network portals. A network portal is a component within a network entity that is responsible for the TCP/IP protocol stack. Network portals consist of an initiator portal that is identified by its IP address, and a target portal that is identified by its IP address and listening port. An initiator makes a connection to the target at the specified port, creating an iSCSI session. An iSCSI initiator or target identified by its iSCSI address is known as an iSCSI node. A portal group is a set of network portals that support an iSCSI session that is made up of multiple connections over different network portals. iSCSI supports multiple TCP connections within a session. Each session can be across multiple network portals. Similar to DNS in the IP world, iSNS acts like a query database in the iSCSI world. iSCSI initiators can query the iSNS and discover iSCSI targets.
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