Networking in Server Racks

Good Day all,

As I understand that it is not advised to use SFP Moduals and fiber to link the servers and the switch in the router, one should use DAC cable.

My question is, is it right to use DAC Cables with in the network cabinet to link all the switches to the 10GB network switch and then use 2x 10GBps SFP and fiber links to link the server rack back to the main network switch?

Thank you in advance.

It really doesn’t matter, in fact, you will get slightly less latency using DAC vs fiber optic because of the processing on the fiber modules. However, the discrepancy in latency is on the nanosecond scale and the measurable difference would be negligible with a small rack deployment. In short, DAC cables have the speed edge over fiber when it comes to latency, and speed is exacerbated when it comes to short runs because of the latency introduced by the fiber modules which propagate the signal. Save your money and just cable your switches up with DAC. Word of caution, if using Cisco, you will need Cisco branded SFP or SFP+ modules.

DAC also uses less power and therefore less heat is generated. If DAC will reach then use DAC. :slight_smile:

Thank you for all the advice so far, Tom, the distance between the 2 switches is 20 meters, I can only get 1 and 3 meter DAC Cables from my IT supplier.

DAC cables are limited to the length they work at, you might want to read about them in more detail, such as here What Is DAC Cable, Direct Attach SFP+ Cable Passive vs Active | FS Community But for the distance you’re looking at I don’t think DAC is your best option.

The maxium lenght for active DAC cables is 10m (7m for passive DAC cables). For longer distances you could use SFP+ 10GBASE-T modules with a RJ-45 connector. These usually support 10G over distannces of ~30m with CAT6a cables, maybe more depending on the manufactuer of the module / switch. But I would recommend using fiber, because it uses less power and therefore generates less heat, and it’s probably cheaper too.

fs.com will program their SFPs to be Cisco compatible

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