Fibre Channnel FC SAN Fabric Overview.

A fabric is a logically defined space in which Fibre Channel nodes can communicate with each other. A fabric can be created using just a single switch, or a group of switches connected together. The primary function of the fabric is to receive FC data frames from a source port (device) and route them to the destination port (device) whose address identifier is specified in the FC frames. Each port (device) is physically attached through a link to the fabric. Many models of switches can participate in only a single fabric. Some newer switches have the capability to participate simultaneously in multiple fabrics. Within a fabric, each participating switch must have a unique identifier called its Domain ID. A SAN provides two primary capabilities: block-level storage connectivity from a host to a storage frame or array, and block-level storage connectivity between storage frames or arrays.

In a Fibre Channel SAN, block requests are handled by a Fibre Channel HBA or Host-Based Adapter. A Fibre Channel HBA is a standard PCI or Sbus peripheral card on the host computer, just like a SCSI adapter. For most typical SAN installations, Fabric connect via switches (FC-SW) is the appropriate choice of Fibre Channel topology. Unlike a loop configuration, a switched fabric provides scalability, and dedicated bandwidth between any given pair of inter-connected devices. FC-SW uses a 24-bit address (called the Fibre Channel Address) to route traffic, and can accommodate as many as 15 million devices in a single fabric. Adding or removing devices in a switched fabric does not affect ongoing traffic between other unrelated devices.

An Overview on EMC IP SANs Architecture.

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.