[c-nsp] Nexus 7k F2E line cards vs F3 vs M3

[Andrey Kostin]

Faced the similar issue with massive discards in VoQ on N7K from F3 on 
ingress to F2E on egress. Never resolved, discards are seen even when 
the traffic is at minimum level but not so critical as it was. In my 
case egress queues didn't show any drops, all discards happened on 
ingress in VoQ, and they were affecting only specific traffic flows.
TAC case was opened and changed three engineers over more than a year 
now, still no useful outcome. Understand that this is probably not very 
helpful for your situation but we were considering switch replacement 
and meanwhile also changing network topology (which was partially done 
in fact as a temporary workaround).
IMHO number of queues looks as not very important parameter because 
affected traffic flows should always go to the same queue, so in theory 
more queues won't ease the back pressure to VoQs, that are also should 
be the same for a particular traffic class.

Kind regards,
Andrey


Curtis Piehler писал 2020-07-13 16:31:
> As it appears the F2E line cards are terrible at dequeuing packets 
> quick
> enough across a port-channeled application.  There was an incident 
> where
> traffic got pinned to one link from the same source/destination causing
> input discards due to back pressure from VoQ drops/congestion on some
> port-channel egress ports.  The issue went away on its own and
> correlated to a sudden increase in traffic (sessions per second)  
> between a
> single source and destination.  All ingress and egress ports are
> port-channeled with at least two members in them.
> 
> Looking at the F3 line cards they have about 7k more egress queue per 
> port
> and double the amount of egress queue per SOC (512k vs 256k).  Granted 
> the
> F3 lines are a huge cost increase would they be an appropriate upgrade 
> to
> handle this type of burst traffic?
> ss quese
> I see the Nexus 7k platform has M3 line cards which cost 3x-4x F3 line
> cards.  What is typically used in data center environments these days 
> ines
> Nexus 7k switches that handle voice applications and such?
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