Chapter 1. Features of the Fibre Channel Hub

The Fibre Channel Hub is a managed 10-port gigabit interface hub for Silicon Graphics FibreVault or fibre channel arbitrated loop (FC-AL) storage clusters or networks, whether RAID or non-RAID (JBOD, or “just a bunch of disks”).

This chapter explains

For more information on fibre channel basics, see the Origin FibreVault and Fibre Channel RAID Owner's Guide.

For information on using the administrative interfaces for a Silicon Graphics fibre channel storage configuration, see the Origin FibreVault and Fibre Channel RAID Administrator's Guide.

Note: The Fibre Channel Hub is transparent and thus does not appear in the fibre channel storage software's administrative interfaces.

Fibre Channel Hub Kit

The Fibre Channel Hub option kit (FC-HUB) contains the following:

  • Fibre Channel Hub

  • four hub feet on peel-off backing

  • standard power cord

    This power cord accommodates United States power outlets only.

  • serial 10-meter (32.8 feet) copper console cable

    This cable is required for connecting the hub to a PC or terminal for management purposes. The cable has an RJ-11 connector at each end.

  • two DB-9/RJ11 adapters

    These adapters are supplied to accommodate PC serial connectors.

  • this manual

Figure 1-1 shows FC-HUB kit contents.

Figure 1-1. FC-HUB Kit Contents

A different power cord with a special connector for the Fibre Channel Rack power distribution unit (PDU) is supplied in the rackmount kit.

If any parts described in this section are missing, contact your service provider.

Appendix C contains a checklist for setting up the hub, with references to specific parts of this guide.

Fibre Channel Hub Physical Features

Figure 1-2 shows the Fibre Channel Hub in a typical application.

Figure 1-2. Fibre Channel Hub, Desktop Use

The Fibre Channel Hub can be used as a desktop unit or can be mounted in a Silicon Graphics Fibre Channel Rack that is not fully configured, or in a third-party standard 19-inch rack (such as a rack used for networking equipment) using the optional rackmounting kit. Figure 1-3 shows two Fibre Channel Hub units in a Fibre Channel Rack. (Cabling to hosts is not shown.)

Figure 1-3. Fibre Channel Rack: Rear View, With Two Fibre Channel Hub Units

See “Fibre Channel Hub Rackmounting Requirements” for information on using the Fibre Channel Hub in a rack.

This section explains

Connectors and Ports

The Fibre Channel Hub has these connectors and ports:

  • one 10-Base-T Ethernet management port, on the front panel

    The Fibre Channel Hub Ethernet management port does not support 100-Base-T.

  • one serial console port, on the front panel, for connection to a host for management purposes

  • one power connector for the hub, on the rear panel

    This connector is autoranging. A power on/off switch is located above the power cord socket on the Fibre Channel Hub, as shown in Figure 1-4. See “System Specifications” in Appendix A for voltage and power requirements.

  • ten copper DB-9 fibre channel ports, all fully digital

    All ten ports are functionally identical.

    For any of these ports, you can use copper or fibre optic cabling. Fibre optic cabling requires a media interface adapter (MIA) at each end of the cable. See “Compatibilities, Fibre Channel Cables, and Adapters”.

Figure 1-4 points out the connectors and ports.

Figure 1-4. Fibre Channel Hub Ports

All ten fibre channel ports are hot-pluggable: you can disconnect a server or storage option from the hub without powering off the hub or the server or storage option.

All ten ports are hot-cascadable: you need not power off the hub to attach the cascade cable to connect two hubs into an 18-port loop. This cable (marketing code FC-HUB-CBL) has two DB-9 connectors and is 51 cm (20 inches) long, including connectors.


On the Fibre Channel Hub front panel are LEDs for each port and for the Ethernet port and network connections. Figure 1-5 points out the LEDs.

Figure 1-5. Fibre Channel Hub LEDs (Front Panel)

Table 1-1 summarizes LED functions for the network and power LEDs.

Table 1-1. Power and Network LED Functionality








Left of 10-Base-T socket; top

On, steady
High intensity, blinking

No power is applied
Power is applied
Segmented hub



Left of 10-Base-T socket; bottom

Low intensity, steady
High intensity, blinking

No connection to network
Link up
Network activity

Table 1-2 summarizes fibre channel port LED functions.

Table 1-2. Fibre Channel Port LED Functionality

Color or State



Forced bypass (accomplished via hub management software)


Port is bypassed: no device is cabled, or there is a problem between source and target


Link between port and another device is established (link up); arbitrated loop is intact

Note: A cable connected to a port does not constitute a valid link unless its other end is connected to a device.

Fibre Channel Hub Rackmounting Requirements

The Fibre Channel Hub can be mounted in a rack using the optional rackmounting kit (marketing code FC-HUB-R). The shelf included in the rackmounting kit accommodates two Fibre Channel Hub devices side by side.

Note: A qualified Silicon Graphics System support Engineer must install the mounting shelf and hub(s) in a rack.

The shelf and hubs fit in the following racks that have the required space:

  • a Silicon Graphics Fibre Channel Rack that is not fully configured

    If the Fibre Channel Rack cannot accommodate the rackmounting shelf and hub(s), you can set up the hub as a desktop unit for use with that storage.

  • a third-party standard 19-inch rack (such as a rack used for networking equipment)

Note: For airflow reasons, the Origin Rack cannot accommodate the Fibre Channel rackmounting shelf and hub(s). To use the Fibre Channel Hub with the Origin Rack, set it up as a desktop unit outside the Origin Rack.

Fibre Channel Hub height is 4.3 cm, or 1.69 inches. The shelf and hub(s) fit in a 1U space (4.45 cm, or 1.75 inches). However, if cabling is routed across the top of the hub(s), an additional space of 1U to 2U is required, depending on the clearances required for such cabling. Thus the total space required for the Fibre Channel Hub in a rack can be as much as 3U (13.35 cm, or 5.25 inches).

A special power cord is included in the rackmount kit for connection to the Fibre Channel Rack power distribution unit (PDU). The sockets of the Fibre Channel Rack PDU require a special connector.

Compatibilities, Fibre Channel Cables, and Adapters

This section consists of the following subsections:

Note: The Fibre Channel Hub operates with Silicon Graphics systems running IRIX 6.4 or later.

Fibre Channel Disk Drives

Table 1-3 lists some fibre channel disk drives that are compatible with the Fibre Channel Hub.

Table 1-3. Some Fibre Channel Disk Drives Compatible With the Fibre Channel Hub

Disk Type


Sectors (Bytes)

Part Number

Marketing Code


18 GB





9 GB; 10,000 rpm





8.8 GB





17.8 GB





8.8 GB; 10,000 rpm




This information is subject to change; check with your service provider.

Note: The 9.1 GB 7200 rpm JBOD disk drive (P-F-9, 9470140) is not compatible with the Fibre Channel Hub. The Fibre Channel Hub does not support the K5+ storage processor.

Fibre Channel Cabling Options for the Hub

The native interface for Silicon Graphics FC-AL disk drive enclosures and for fibre channel XIO and PCI interface boards is a female copper DB-9 connector. For technical details of Fibre Channel Hub connectors, see Appendix A, “Technical Specifications.”

The Fibre Channel Hub accepts copper and optical cabling options:

  • for distances up to 30 meters: ANSI-compliant copper twinax cable assemblies

  • for distances of 10 to 300 meters: fiber optic cable assemblies, using media interface adapters (MIAs)

    Distances longer than 300 m require special MIAs and special cables.

    MIAs are described in “Media Interface Adapter (MIA)”.

It is recommended that you use fibre channel cabling from Silicon Graphics for the Fibre Channel Hub. Table 1-4 summarizes fibre channel interface cables currently available from Silicon Graphics that are compatible with the Fibre Channel Hub.

Table 1-4. Fibre Channel Cabling Options: Codes and Part Numbers



Marketing Code

FC copper cable with 9-pin DIN

0.3 m (.98 ft)



10 m (32.8 ft)



25 m (82 ft)


FC optical cable (requires X-F-OE-KIT)

3 m (9.84 ft)



10 m (32.8 ft)



25 m (82 ft)



100 m (328 ft)



300 m (984 ft)


Two media interface adapter (MIA) modules
(FC copper-to-optical)



Silicon Graphics fiber optic cables and MIAs are 62.5/125 μm (multimode).

Media Interface Adapter (MIA)

To connect fiber optic cable to one of the copper ports on the Fiber Channel Hub, use a media interface adapter (MIA). This adapter converts from a fiber optic cable with an SC connector to a copper DB-9 connector, providing a non-Open Fibre Control optical link.
Silicon Graphics supplies the MIA in pairs.

The MIA is a full-duplex module that converts photons to electrons in one direction and converts electrons to photons in the other direction. An industry-standard duplex SC connector supplies the external fiber-optic connection on the MIA. The Fibre Channel Hub powers the MIA, which converts the differential electrical signal into light for transmission through the fiber optic cable. The MIA has a DB-9 male plug on one end, which connects to the hub, and an optical SC connector on the other end, which connects to any fiber optic cable assembly or jumper cable. Figure 1-6 shows the MIA.

Figure 1-6. Media Interface Adapter (Optional)

At the other end of the fibre optic cable, another MIA converts the signal back to a differential electrical signal for the system to which it is attached.

Note: It is recommended that you use MIAs from Silicon Graphics for fibre optic cabling with the Fibre Channel Hub.

Fault and Error Management

The digital architecture of the Fibre Channel Hub eliminates all signal jitter and provides automatic clock speed matching on every port. As a result, two hubs can be cascaded, providing flexibility in network design and extending potential cabling distances.

Fibre Channel Hub error management improves the reliability and availability of fibre channel arbitrated loops by isolating faults that could damage the rest of the loop, and correcting error conditions that could cause loop downtime.

  • Loop initialization procedure (LIP) F8 bypass isolates faulty nodes, allowing the loop to operate normally while cabling problems and other errors are diagnosed and corrected. LIP F8 character streaming is described in greater detail in “Automatic LIP F8 Word Substitution and Bypass.”

  • Synchronous cut-in and cut-out ensure that only complete words are forwarded through the hub. Character integrity control ensures that only valid Fibre Channel words are forwarded through the hub. Thus, recovery issues in remote devices are avoided.

  • Automatic LIP insertion notifies all loop participants when nodes are added or when active loops are combined. Automatic LIP insertion is described in greater detail in “Automatic Loop Reconfiguration”.

Automatic LIP F8 Word Substitution and Bypass

If a hub port receives three consecutive LIP F8 primitive sequences from an attached device, the port automatically enters bypass mode.

LIP F8 sequences slow the loop or make it nonfunctional. However, by default, the Fibre Channel Hub automatically bypasses a port that is streaming LIP F8 characters. The port's status is shown as auto-bypass in the Hub Port Status screen and in the output of the show port command.

When LIP F8 bypass occurs, the hub transmits LIP F0s and IDLEs to keep the loop alive. Thus, LIP F8 sequences do not enter the loop.

The attached device is determined to be functional again when the LIP F0 sequence can be propagated. When the device no longer sends LIP F8 sequences and the port receives valid data again, the hub software reinserts the port into the loop by sending LIP F7 F7.

Automatic Loop Reconfiguration

AutoLIP (Originate LIP F7 on insertion) automatically reconfigures the loop when a hub port becomes active.

Any change in loop membership requires loop reconfiguration. Normally, loop reconfiguration is triggered when a device transmitting an LIP F7 F7 sequence is inserted into a loop.

When a port comes out of bypass, it automatically inserts LIP F7 F7 into the loop until the device attached to the port sends a LIP sequence other than LIP F8.

When two hubs are cascaded, there is no “device” to sense insertion. The Fibre Channel Hub uses the AutoLIP option, so that it can insert the necessary LIP F7 sequence when it is connected to another hub.

Also, after a port comes out of bypass and before the port is reinserted into the loop, the hub port automatically inserts LIP F7 into the loop until a LIP sequence (other than LIP F8) is received.

Loop Management Software

The Fibre Channel Hub software provides statistics for each port detailing the number of invalid transmission words, comparative error rates, and port down counts. You can use the management tools to reconfigure the loop remotely to optimize performance or to diagnose and isolate failures. You can view port operation statistics, force-bypass a port, join two loops or separate a loop into two loops, change passwords, or perform other management tasks.

Included with the Fibre Channel Hub are these interfaces for managing loops:

  • HTML interface, compatible with most standard Web browsers

  • command-line interface for use via a local console or Telnet connection

  • SNMP agent interface

For complete information on software configuration and management of the hub, see Chapter 4, “Setting Up Local or Remote Hub Management,” and Chapter 5, “Fibre Channel Hub Operation and Management.”

You can manage the hub:

Requirements for setting up these management options are in “Determining Hub Management” in Chapter 2.