Technical information

GALAXY® AUROURA LS CONFIGURATION AND SYSTEM INTEGRATION GUIDE
83 Section 4 Troubleshooting Guide
4.15 Fibre Host connectivity issues
Of all of the possible cables in Aurora LS’s RAID system, by far, the most delicate are Fibre
Channel cables. The amount of problems that is possible with these cables is somewhat
astronomical compared with other cables. First a description of how they are constructed:
There are two optical conduits in a standard LC cable, one carrying light to the array’s SFP,
and one bringing light back. The diameter of this conduit is much larger than the width of the
laser beam projected into it, but the cable is designed to bounce the beam off the inner sides
of the fibre conduit. At the ends of these conduits are a pair or lenses. These lenses are glued
on carefully, by hand, and do two things: 1) Protect the ends of the fibre conduit itself, and 2)
Focus the beam to a point going in or out. The lenses can occasionally get misaligned or
move during the glue’s curing process. Everything surrounding the lenses (just about) is
plastic. Two mechanical problems which can occur are because of this plastic: It’s possible
that a cable may be misassembled by putting the wrong lens on the wrong conduit, flipping
one end of the cable upside-down. The way to tell if this is occurring is to plug the cable into
an operating Fibre channel device, and compare the other end to what it is plugging into – if
the laser on what it is plugging into is coming from the same side as the laser coming from the
cable, the cable is defective. The other mechanical problem – the plastic portion of the plugs
can be broken easily, so care must be used when inserting or especially when removing the
cables. Now the cable itself is made of fiberglass, which is essentially plastic. If you took a
clear semi-thick piece of plastic and bent it, you would find that where it bends, it turns opaque
(white), and you can’t see through that part. It is similar with the fibre itself – you don’t want to
bend it if possible – I’d say you don’t want to go around a bend with an equivalent diameter
less than a 3 inch circle. If it is bent too far, although you won’t be able to see it, the cable
inside will turn opaque, preventing the beam from passing through properly. If this happens,
the cable is useless. When the Fibre cables or cards are shipped, they have protective covers.
The cover on the card is mainly to keep dust out (If dust gets in-between the emitter/detector
and the lens, it might impair data transmission). However the covers on the cable are for a
different reason – to protect the lenses from getting scratched. If the lenses on the cable
become scratched, they will also impair the ability for the cable to carry the light from the laser.
4.16 Troubleshooting Aurora LS’s Client Related Problems
Fibre Based Clients
Assuming there are no problems on the array, in order for a client to be able to see a LUN,
there is a certain chain of items which must be present as in the following diagram: