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As shown in Figure 8-2, the hardware components of a Fibre Channel implementation can include the following:
Figure 8-2. RA4X00 configuration.8.3.1 Host Bus AdaptersA Fibre Channel host bus adapter (HBA), shown in Figure 8-3, translates SCSI commands into serial data that can then be converted to light by GBICs. A GBIC is a transceiver that converts serial electrical signals to and from serial optical signals. In a network, a GBIC is used to transmit data across Fibre Channel media. Figure 8-3. Fibre Channel host bus adapters.Most Fibre Channel HBAs use GBICs or GLMs. Like GBICs, GLMs convert electrical signals to and from optical signals, but they also convert serial signals to and from parallel signals. A typical HBA uses the PCI bus, which in turn uses a highly integrated application-specific integrated circuit (ASIC) for processing the Fibre Channel protocol and managing the I/O with the host. Each server can have one or two HBAs. The number of HBAs that can be configured in each node limits the maximum number of storage arrays. Note The operating system detects the HBA as a SCSI controller, not as a Fibre Channel network interface card (NIC). Therefore, it should be configured using the operating system, just as other SCSI controller cards are configured. 8.3.2 Gigabit Interface ConvertersThe GBIC translates the electrical impulse into the optical signal used with the fiber-optic medium. It contains a device that emits an optical signal used for transmission along the fiber-optic cable. Each Fibre Channel link requires two GBICs, one at each end of the fiber-optic cable, as shown in Figure 8-4. Figure 8-4. GBICs attached to a fiber-optic cable.The GBIC module installs in a special receptacle on the following components:
The GBICs have two channels, one for each optical fiber within the cable (link). Therefore, each GBIC module is a full-duplex transmission device. Figure 8-5. How GBICs work.8.3.2.1 HOW GBICS WORKA GBIC converts serial electrical signals to and from serial optical signals for transmission of data across the Fibre Channel media. When using Fibre Channel as the communication medium, the signal must go through two types of conversion: parallel to serial, and electrical to optical. With parallel to serial, the parallel signals generated by the host or the target storage device must be converted into serial (Fibre Channel) signals. With electrical to optical, the electrical signal generated by the host or the target storage device must also be converted into an optical signal used by the optical Fibre Channel medium. 8.3.2.2 GBIC SHORTWAVEGBIC shortwave (GBIC-SW) is a shortwave version of the GBIC module that supports the multimode fiber. The following table shows the GBIC-SW specifications.
8.3.2.3 GBIC LONGWAVEGBIC longwave (GBIC-LW) is a longwave version of the GBIC module that supports the single-mode fiber. GBIC-LWs have the following specifications.
8.3.3 Gigabit Link ModulesGigabit link modules, or GLMs, are highly integrated fiber-optic transceivers that provide high-speed, bidirectional continuous throughput. They are similar to GBICs because they convert electrical signals to and from optical signals. However, GLMs also convert serial signals to and from parallel signals. Figure 8-6 shows a typical GLM. Figure 8-6. Gigabit link module.One GLM at each end of a point-to-point duplex configuration plugs into a host card such as an HBA or a Fibre Channel hub or switch. The 64-bit/33MHz HBAs use GLMs rather than GBICs. Either single-mode or multimode Fibre Channel SC duplex connectors can be inserted into the ports of the GLM. Like GBICs, GLMs are available in both longwave and shortwave configurations. 8.3.4 Fibre Channel HubsHubs link individual elements together to form a loop with shared bandwidth. They share the following characteristics:
Hubs perform several functions:
8.3.5 Fibre Channel SwitchesA switch interconnects multiple nodes. A network of switches in a Fibre Channel environment, which can include as many as 16 million nodes, is referred to as a fabric. Nodes connect to this fabric to access other nodes. A switch typically uses packet switching. The switch divides each message into small sections called packets and adds the network address of the sender and destination to each packet. The packets can take any route to the destination and are reassembled for delivery. The primary function of a switch is to receive frames from a source node and route them to a destination node. Each node has a unique Fibre Channel address, which the switch uses to route frames. The switch relieves each individual port of the responsibility for station management. Each node manages only a simple point-to-point connection between itself and the switch. Nodes can be servers, storage devices, or another device that communicates through the network. Here are some key points to remember about a Fibre Channel switch:
8.3.5.1 FIBRE CHANNEL SWITCH ZONINGZoning is a method of segregating storage I/O traffic between groups of servers and their associated storage subsystems. The zoning types are as follows:
Each zone has a member list consisting of one or more zone members. Members of a zone can be specified through node World Wide Name (WWN), port WWN, or switch domain ID and port number. A Fibre Channel switch-zoning configuration is shown in Figure 8-7. Figure 8-7. Fibre Channel switch zoning.A device can be a member of multiple zones. However, when zoning has been enabled, every device in the fabric must be part of a zone or zones. Note When zoning has been implemented in a SAN, the zoning information will need to be changed each time a server or storage subsystem is added or removed. HBA replacement also requires a zoning information update. 8.3.6 Comparing Hubs and SwitchesUntil recently, hubs have been the entry-level devices for connectivity because they are relatively low in cost and simple to integrate. Switches are just as easy to install as hubs, but offer superior connectivity. Fibre Channel switches provide scalable systems of almost any size, unlike hubs that have a 127-node limit. Figure 8-8 shows placement of hubs and switches. Figure 8-8. Placement of Fibre Channel hubs and switches.The following table compares the use of hubs and switches in Fibre Channel networks.
8.3.7 Guidelines for Choosing Between Switches and HubsUse hubs in the following situations:
Use switches in these situations:
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