Buffer on 10gig switches

[CrackedJack1]

I'm looking into 10gig switches was surprised to see their shared buffers seem to be lower than 1gig models.

For example, a nexus 3000 series has a smaller buffer than a 4948.

Would I be correct in assuming that on a 10gig switch the amount of traffic can be so great that you would need huge buffers to absorb any spike that exceeded the 10gigs. As a result the switches only provide a small amount of buffer just in case to handle a very tiny burst but 10gig is just to much traffic to buffer?

Another example is the 4500x which says it has 32mb which is easily twice that of a nexus 3000 or an Arista or hp 5900 series switch. Why would the 4500x, a 10gig switch, have such a large buffer compared to most other 10gig switches especially the nexus which I thought was the next step above the 4500x?

[Philip D'Ath]

The Cisco 3850 10Gbe switches have some of the best buffering in the mid-range Cisco switch options.

The Nexus 3k has very low buffering.  It is great for 10Gbe to 10Gbe (can do cut through switching).  However it goes terribly if you have say 10Gbe storage feeding a 1Gbe connected server (you'll get lots of dropped packets).

Basically, you mostly need buffering when you have an 10Gbe ingress port feeding 1Gb/s egress ports.  The inbound data arrives much faster than it can be sent.

Cisco 3850's and 4500's are designed to support lots of 1Gbe ports - so lots of buffering.  While you can plug a Gbe SFP into a Nexus 3K - it is designed for 10Gbe switching.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Basically, you mostly need buffering when you have an 10Gbe ingress port feeding 1Gb/s egress ports.  The inbound data arrives much faster than it can be sent.

True, but more ingress ports to less egress ports, even when same speed, also often creates a need for buffering too.  However, unlike a higher bandwidth ingress port, to a lower bandwidth egress port, the greater to lessor number of same bandwidth ports depends on overall aggregate utilization of the ingress ports.