10GE TOR port buffers (was Re: 10G switch recommendaton)

Joel jaeggli joelja at bogus.com
Fri Jan 27 23:38:53 UTC 2012

On 1/27/12 15:01 , George Bonser wrote:
>> -----Original Message----- From: bas Sent: Friday, January 27, 2012
>> 2:54 PM To: George Bonser Subject: Re: 10GE TOR port buffers (was
>> Re: 10G switch recommendaton)
>> While I agree _again_!!!!!
>> It does not explain why TOR boxes have little buffers and chassis
>> box have many.....
> Because that is what customers think they want so that is what they
> sell.  Customers don't realize that the added buffers are killing
> performance.

It is possible, trivial in fact to buy a switch that has a buffer too
small to provide stable performance at some high fraction of it's uplink
utilization. You can differentiate between the enterprise/soho 1gig
switch you bought to support your ip-phones and wireless APs and the
datacenter spec 1u tor along these lines.

It is also possible and in fact easy to have enough to accumulate
latency in places where you should be discarding packets earlier.

I'd rather not be in either situation, but in the later I can police my
way out of it.

> I have had network sales reps tell me "you want this switch over
> here, it has bigger buffers" when that is exactly the opposite of
> what I want unless I am sending a bunch of UDP through very brief
> microbursts.  If you are sending TCP streams, what you want is less
> buffering. Spend the extra money on more bandwidth to relieve the
> congestion.
> Going to 4 10G aggregated uplinks instead of 2 might get you a much
> better performance boost than increasing buffers.  But it really
> depends on the end to end application.

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