Aside from the obvious cabling mess you avoid (which I know for us as network engineers is great, but hard to use as an excuse when reasoning with someone who sees no point in it), what do you gain versus copper straight through to a larger core?
Context:
– Price is of no concern
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Company had already decided on a dual Nexus core.
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Option 1: Nexus 7004's, which would be nearly fully populated with 10G SFP+ and aggregate connections to several FEXs at the top of each rack in the DC, as well as aggregate SAN and various server connections
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Option 2: Nexus 7009 cores that will be approx. 1/3 filled up with various modules to accommodate the aggregation of all fiber connections from all devices.
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This is a colocated data center
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Standard call center/enterprise domain related services hosted on the network
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QoS is a very important bulletpoint to emphasize given that this company is a call center
Problem:
- I am unable to justify going with Cisco's "top of rack" setup despite my wanting less of a cabling mess and a more modular design. I'm unable to do so because you are inserting a point of failure into the network. Doing this increases the latency (even if it's only by a small amount), etc. Not only that, but now that I think about it, since all FEXs rely on the Nexus to operate, you not only increase the chance of a hardware failure bringing down a block of devices, but now a software process that could wig out and cause the FEX to malfunction in some way.
So, before I put the top of rack design in the idea graveyard for this project, can anyone else see a reason not to go with a larger core and no FEXs given the lack of budget limitation?
Best Answer
Keep in mind that a FEX inherently is a method by which to extend the fabric, thus the name. The ability to manage centrally while still having "line cards" distributed throughout the DC is the real reason to use a FEX. Drastically reducing cabling is valuable to anyone, technical or not, and the argument of being able to manage the entire infrastructure at fewer points is time savings, pure and simple.
One of your big doubts is that you're worried about single points of failure. All devices have the ability to be dual-homed, and in certain configurations, you can even establish virtual port channels with the Nexus 2K FEXs themselves.
Take a look at Cisco's documentation. You'll find that you can design a topology that is just as redundant as the "direct-cable" option you're considering, with less fuss.