We have 7 switches in one rack that are all connected to each other via SFP mini GBIC fiber connections running at 1GBps.

I know fiber provides benefits in terms of extending the distance that cables can be run between switches but since the switches are right next to each other is there any difference in performance or other reasons why I would want to use fiber to connect these switches instead of cat 5e with a 1 GBps Ethernet connection?


Technically there's increased latency by running Cat5/6 wire vs Fiber or direct Copper GBICs. But the latency is in the order of microseconds and unless you're running a HPC isn't usually worth mentioning.

  • So barring HPC, which we are not doing, your answer would be that there is no difference and it would be essentially the same for us to have these switches connected via Ethernet instead of fiber? – Chris Magnuson Jan 19 '11 at 15:56
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    I would say yes to that question, and if you need more bandwidth between switches you can configure aggregate links. – SpacemanSpiff Jan 19 '11 at 16:03

One thing to keep in mind is that there is a minimum length for copper wires, go under that and you'll start seeing more cross-talk, causing lower performance. There may be a lower length for optical fibres as well, but these days the optics in SFPs and GBICs tend to be able to take a fair bit of over-light without too much of a problem.

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    You'd need optical attenuators to drop the light source down (measure with a power meter) within tolerance for the GBIC. But for short cable runs I've had to run a 10' cable for a 6" run. This can be more cost-effective because of the cost of the optics to light up short circuits. – Nick Zepp Jan 21 '11 at 14:40

No attenuators needed on multimode and any performance difference is on the order of fractions of a microsecond, which is well below the tolerance level even for tightly coupled HPC.

Go with the cat5e. It is cheaper, easier to work with and will easily fit the bill.

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