Fiber patch cables seem to be very forgiving, when light shines through everything is great and everybody’s happy, right? Wrong!!!
You shouldn’t underestimate the importance of keeping the ends of patch cables and the SFPs clean, since the actual diameter of a fiber is either 9 or 50 (or even 62.5) mu (micron).
Light travels through fiber seemingly undisturbed, but little pieces of dust or dirt will reflect the light away from the core and much of the total “light power” is lost. This can significantly reduce the ability to cross large distances or even fail the transmission of light all together!
A single speck of dust can be disastrous for the beam of light that needs to be sent through to the other side. Through a microscope you can clearly see the scale of dirt on the actual core:
When not using a fiber SFP or fiber patch cable, please use the protective cover or cap to prevent (as much as possible) dirt from sticking to the optic ends. Each cable always comes with a cap and each SFP is always protected by a little rubber cap as well. Do not remove until a cable is plugged into the SFP and place this rubber cap back when no cable is plugged in!
Leaving a patch cable unprotected is simply asking for it! Dirt will easily stick to the optic ends and the next person to use a cable will face the possible problems of errors on the connection or even failed links.
Keep fibers clean and keep everything working!
In 2010 EMC ran a pilot (read it!) to look at the consequences of dirty cables in the SAN and what they found was scary! EMC bought and started using fibre inspection equipment to avoid negative results of using dirty fibers.
Although it’s very clear and proven that dust in a “light” environment doesn’t go well together, it’s still received with a lot skepticism. In the industry in general I note Cisco have quite a detailed write up on contamination in their best practice guides however Brocade mention it in theirs but have little detail. Luckily the community is picking it up fast and (at least) I see that more people start protecting their fibers better than they used to.
So this is an example of what a fiber connection looks like before and after cleaning it: