We have 5 3com 4200 switches forming a ring (connected using 10GBase-CX4 XENPAK modules) and would like to add a few servers with 10GbE adapters soon.
The offer we are currently looking at consists of a Voltaire 6024 10GbE switch and various transceivers so we can add it to our ring:
- 2 SFP+ 10Gbase-SR transceivers for the Voltaire switch
- Fibre cables (LC-LC)
- 10Gbase-SR to XFP transceiver for the 3Coms
- 1-Port 10G XFP modules for the 3Coms
Alternatively, we could break up the ring and connect each of the 3Com switches to the Voltaire using these components so we get 10GbE for each of our 3Coms instead of for all of them together.
Is this a good solution? What kind of overhead should we expect from using SFP+ => 10Gbase-SR => XFP => 3com switches?
Ideally, we would like to use SFP+ (for NICs and the switch), but if CX4 etc. offers some advantages in this situation, we can still change that and purchase other components.
There isn't really any substantial overhead by SFP+ to XR, unless I'm really misunderstanding your question. 10GE is 1GE for 99% for all applications. There are obviously some underpowered switches that can't do wirespeed, but that depends on what sort of traffic you're expecting.
As far as your topology, it sounds like now you have A-B-C-D-E-A and you're trying to figure out if it's better to connect each of A-B-C-D-E directly to F instead of to each other. It really depends on your traffic pattern and how your STP is running right now. You obviously lose a great deal of redundancy by having F be the center switch, but in a ring you lose a lot of throughput as well. It depends on your needs.