IBM System Storage DS4000, Hardware Maintenance Manual, Page: 32 / 184

General checkout
Installation and operational problems in an arbitrated loop environment are
typically caused by one of the following situations:
v Faulty cabling or cable connector
v Incorrect cable plugging
v
Faulty GBIC
v Faulty hubs
v
Invalid fibre channel signaling from the host bus adapter (HBA) or disk array
v
Device driver or microcode conflicts between the HBAs and other devices
The following information will help you to isolate and correct the physical layer
problems. For protocol-related problems, such as inoperability between devices, see
the documentation that came with the individual devices.
Port Status LEDs
The hub provides two status LEDs for each port (see Table 8). Use these LEDs to
help you quickly diagnose and recover from problems.
The upper, green LED is lit when an operational GBIC is installed. The lower,
amber LED is lit when the port is in the bypass mode. In the bypass mode, a port
is disabled, which prevents erratic signals or data from disrupting loop activity.
The bypass mode could be triggered by the loss of a valid signal or by a GBIC
fault. The combination of green and amber LEDs indicates one of the four
following states.
Table 8. Type 3523 fibre channel hub port status LEDs
Green LED Amber LED Port State
Off Off No GBIC Installed
On Off Operational GBIC; Valid Signal
Off On Faulty GBIC; Port Bypassed
On On Operational GBIC; No Valid Signal; Port Bypassed
Verifying GBIC and cable signal presence
Note: Do not look directly into any fiber cable or GBIC optical output. To view an
optical signal, use a mirror to view the reflected light.
Verifying signal presence
In addition to verifying port LED status, you can verify signal presence by using a
mirror to look for a reflected light at the fiber-optic cable ends and the GBIC
transmitter. To verify signal presence at the hub end of a link, insert a GBIC into
the hub and place a mirror at the bottom of the SC connector. If a signal is present,
you will see a low intensity red light in the mirror reflecting from the GBIC
transmitter. See Figure 2 on page 5.
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IBM TotalStorage DS4000: Hardware Maintenance Manual