45xx Modular Disk Subsystem Manual for G-Series Releases

Introduction
45xx Modular Disk Subsystem Manual for G-Series Releases—142466
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Fiber-Optic Cables
6760 Adapter and SAC LEDs
Each 6760 adapter has two LEDs indicating hardware status.
•
The green LED indicates that the adapter is powered on, and it is normally lit.
•
The amber LED indicates hardware faults.
The fiber-optic SAC has an amber LED that is lit when fiber-optic light is present. For
troubleshooting information about the 6760 adapter and its SACs, see the 6760
ServerNet/DA Manual.
For detailed troubleshooting information using the LEDs of the disk module BEB,
power supply, and disk drives, see Section 3, Checking Hardware Operation
.
Optical Data Links
Each SAC installed in a 6760 adapter contains one optical data link connector, where
you attach the fiber-optic cable that connects the SAC to the 45xx disk module. The
connector is keyed so that the fiber-optic cable can be installed only one way. (The
optical carrier signal is not visible to the naked eye.)
Fiber-Optic Cables
A fiber-optic cable connects each BEB in a 45xx disk module to a SAC installed in a
6760 adapter in a host system (see Figure 1-9 on page 1-15). The two BEBs in a
455mod8 module connect to two SACs, and the two SACs can be in separate 6760
adapters. This fiber-optic connection cannot exceed 2 Kilometers (1.2 miles).
Tandem supplies standard indoor fiber-optic cables in lengths from 10 meters (32.8 feet)
to 500 meters (1640 feet).
All cables except the 1-meter cable and 10-meter cable are
spooled. For cable part numbers, see the 6760 ServerNet/DA Manual.
For more information on fiber-optic cable specifications and installation, talk to your
Tandem representative about getting the Tandem 1300-nanometer fiber-connected
storage product documents:
•
Specifications for Two-Kilometer Operations (096880)
•
Fiber-Optic Handling and Installation (069363).
Both documents are available from Tandem document control.
Fault Tolerance
Fault-tolerant processing is supported by using primary and backup processors, primary
and backup SACs, primary and backup disk drives with mirrored disk drives.
Figure 1-7
shows two SACs in separate 6760 adapters managing I/O for one 45xx disk
module containing up to eight disk drives.
When two physical disk drives of a mirrored volume are configured to share the same
45xx module, there is a single point of failure possible for both disks. However, when
you configure a mirrored volume so that each disk drive is installed in a separate