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Nexus - FEX performance

Unanswered Question
May 14th, 2014
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If we connect a FEX device to 2 X 6004 Nexus switches with uplinks to each 6004 with VPC as compared to a Cisco L3/L2 switch connected to 2 X 6004 Nexus with trunked-uplinks to each 6004 with VPC, what could be the impact on network speed performance for the hosts connected to FEX or switch ports, especially if the network is to perform in low latency.

Access ports for FEX and Cisco L3/L2 switch is same 1 Gbps-copper.

In both cases the uplink from FEX or switch to 6004 is same (10 G + 10 G ) 20 Gbps.

FEX - Sounds like extending the fabric back-plane of parent 6004 way down to FEX device but still bandwidth is bottle-neck?

Is the protocol with which Nexus 6004 communicates with FEX over VPC- port-channel better than the how it would communicate with VPC-port-channel trunk-port with Cisco switch? (If the combined uplink bandwidth is same in both cases).

Please share the experinece.

Thanks in advance.


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LA-Engineer Wed, 07/23/2014 - 18:42
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The ports on the FEX use a shared buffer and is significantly smaller than the ports on the parent switch.  We had lots of issues with performance when using the FEX for iSCSI.  Also consider that FEX host port to FEX host port traffic has to hairpin through the parent switch.



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