8.3. Fibre Channel Hardware Components

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As shown in Figure 8-2, the hardware components of a Fibre Channel implementation can include the following:

  • Host bus adapters (HBAs)

  • Gigabit interface converters (GBICs)

  • Gigabit link modules (GLMs)

  • Storage and Fibre Channel drive arrays

  • Fibre Channel array controllers

  • Fibre Channel hubs and switches

  • Tape libraries

  • Fibre Channel cables

Figure 8-2. RA4X00 configuration.


8.3.1 Host Bus Adapters

A 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 Converters

The 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:

  • HBA

  • Fibre Channel controller

  • Fibre Channel storage hub

  • Fibre Channel switch

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 WORK

A 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 SHORTWAVE

GBIC shortwave (GBIC-SW) is a shortwave version of the GBIC module that supports the multimode fiber. The following table shows the GBIC-SW specifications.

Feature

Details

Compliance

Fibre Channel FC-PH-2 physical layer option 100-M5-SN-I

Baud rate

1062.5MB/s

Fiber shortwave

50mm diameter (preferred) or 62.5mm multimode fiber

Laser wavelength

780nm (non-OFC)

Optical connector interface

Dual SC

Distance

50m: 2 through 300m per link (International) 62.5m: 2 through 500m per link (North America)


8.3.2.3 GBIC LONGWAVE

GBIC longwave (GBIC-LW) is a longwave version of the GBIC module that supports the single-mode fiber. GBIC-LWs have the following specifications.

Feature

Details

Compliance

Fibre Channel FC-PH-2 physical layer option 100-M5-SN-I

Baud rate

1062.5MB/s

Fiber longwave

9mm single-mode fiber

Laser wavelength

1250nm

Optical connector interface

Dual SC

Distance

10km per link (maximizes cable length per FC-AL to 25km)


8.3.3 Gigabit Link Modules

Gigabit 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 Hubs

Hubs link individual elements together to form a loop with shared bandwidth. They share the following characteristics:

  • Enable the connection of multiple arrays to a single host adapter, which greatly increases the amount of storage available to the server

  • Interconnect loop devices in a physical star topology, in which all workstations are networked to a central computer, providing more convenient wiring and cable management

  • Integrate easily and are relatively low in cost

  • Implement an FC-AL topology

  • Provide connection to a shared 100MB/s FC-AL (half duplex between servers and disks, all sharing bandwidth)

  • Provide more complex error recovery because of loop initializations

  • Detect all traffic that passes between other nodes

Hubs perform several functions:

  • Provide support for single-mode or multimode optical cables

  • Enable hot-swapping of cable interconnects for service or repair

  • Provide increased fault isolation in case of a cable or node failure

  • Provide failure status and traffic monitoring capability

  • Enable implementation of a SAN

8.3.5 Fibre Channel Switches

A 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:

  • A switch implements FC-SW.

  • It provides support for optical cables as long as 500m (10km with longwave GBICs).

  • It enables hot-swapping of cable interconnects for service or repair.

  • It provides increased fault isolation in case of a cable or node failure.

  • It enables implementation of a storage network through Fibre Channel technology.

  • A switch can cascade and make large topologies.

  • A switch uses Simple Network Management Protocol (SNMP) for management and control.

  • It provides a full-duplex 100MB/s point-to-point connection to the Fibre Channel fabric, allowing the servers to use loops (results in improved scaling of loops for optimized performance).

  • It isolates individual nodes from the reconfiguration and error recovery of other nodes within the fabric.

  • It has built-in intelligence.

  • It offers room for growth.

  • It provides multiple methods for switch management.

8.3.5.1 FIBRE CHANNEL SWITCH ZONING

Zoning is a method of segregating storage I/O traffic between groups of servers and their associated storage subsystems.

The zoning types are as follows:

  • Soft zoning The Fibre Channel switch provides filtering to mask ports belonging to a zone from ports that do not belong to a zone.

  • Hard zoning Hard zoning is hardware implemented and physically blocks access to the zone from outside nodes.

  • Port zoning Often port zoning and hard zoning are considered to be the same. However, port zoning is a software implementation that allows unauthorized external access.

  • Broadcast zoning Broadcast zoning filters broadcast messages so that they are not sent to specified ports.

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 Switches

Until 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.

Hubs

Switches

Implement an FC-AL topology with shared bandwidth among all devices.

Provide connection to a shared 100MB/s FC-AL, single 100MB transfer at a time.

Implement an FC-SW topology, with ports for either fabric devices or arbitrated loop devices.

Provide 100MB/s point-to-point connection between devices, multiple 100MB transfers at a time, no multiple device arbitration time.

Performance decreases as nodes are added because of additional arbitration time.

Nodes on the Fibre Channel loop see all traffic going between other nodes.

More complex error recovery because of loop initializations.

No performance reduction as additional nodes are added.

Nodes on the Fabric Channel detect only data destined for themselves.

Individual nodes are isolated from reconfiguration and error recovery of other nodes within the SAN.

More chances for traffic disruption on reconfiguration and errors because of loop initializations.

HP 12-port hubs have optional management.

Fewer chances for traffic disruption on reconfiguration and errors because control features manage loop initialization events.

Provide management control of the Fibre Channel infrastructure.

Seven-step loop initialization process (LIP). If a device encounters an error, it initiates a LIP. Loop is unavailable for data transfer during the error recovery.

Provide greater stability during error recovery.


8.3.7 Guidelines for Choosing Between Switches and Hubs

Use hubs in the following situations:

  • Applications with one to four servers

  • Cost-sensitive Microsoft Windows 2000 applications with a homogeneous platform and operating system environment

  • Applications in which the shared bandwidth of an arbitrated loop configuration is not a limiting factor

Use switches in these situations:

  • Applications with more than four servers

  • Multinode cluster configurations in which traffic disruption because of reconfiguration or repair is a concern

  • "Clusterlike" configurations in which expansion is anticipated

  • Heterogeneous platform and operating system applications

  • High-bandwidth applications in which a shared arbitrated loop topology is not adequate

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    HP ProLiant Servers AIS. Official Study Guide and Desk Reference
    HP ProLiant Servers AIS: Official Study Guide and Desk Reference
    ISBN: 0131467174
    EAN: 2147483647
    Year: 2004
    Pages: 278

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