[NCLUG] Networking Issue

Tue Aug 6 10:06:06 MDT 2013

I suspect "Tx discards" reflect buffer limitations somewhere... which
explains why enabling flow control end-to-end mostly solves the discards
problem but negatively impacts throughput.

I'm not familiar with HP's mesh technology, but if it amounts to link
aggregation without equal-cost load balancing, you may see discards due to
issues with the hashing algorithm.

For 1 Gbps and faster connectivity, I would strongly consider implementing
end-to-end jumbo frames to maximize performance.  Depending on the buffer
architecture, it could positively or negatively impact the discards
problem.  On modern equipment, I've only seen improvements from
implementing it.

P.S. - Isn't the 2500 mostly an ancient 10/100 Mbps switch with limited
support for 1 Gbps?

On Tue, Aug 6, 2013 at 9:06 AM, Michael Coffman
<coffman at ftc.avagotech.com>wrote:

> On Mon, 5 Aug 2013, Matt Kassawara wrote:
>
>  Do both variants of configuration A have the same problem?
>>
>
> Yes.
>
>
>  Do any of the switches in question indicate the reason for discards?
>>
>
> Only the hp5412(b) listed is showing discards.   All it says from what I
> can tell is 'Tx discards'
>
>
>  Did you configure end-to-end support for jumbo frames?
>>
> Jumbo frames are not enabled.
>
>
>  Can you provide more details on "10g mesh" between the 5412s?
>>
>
> We have 3 5412's that are all connected via 10g and have HP's meshing
> enabled.   What kind of detail are you looking for?
>
>
>>
>> On Mon, Aug 5, 2013 at 5:14 PM, Michael Coffman
>> <coffman at ftc.avagotech.com>**wrote:
>>
>>
>>> I don't do networking and our corporate networking group has been cut so
>>> thin, they don't do much networking anymore either :(
>>>
>>> This is not a linux problem, but I know there are folks on this list that
>>> have deep networking experience.  I'll try to describe the problem as
>>> best
>>> as I can in ascii.
>>>
>>> *NA = NetApp
>>> *CS = Compute Server
>>>
>>> #----  A
>>> NA -10g-> hp5412(a) -10g mesh-> hp5412(b) -1g-> CS
>>> NA -10g-> hp5412(a) -10g mesh-> hp5412(b) -4g trunk-> hp2500 -1g-> CS
>>>
>>> o The read path to the compute server is very slow 20-30MB/s
>>> o The write path to the NetApp is close to wire speed 110-130MB/s
>>> o The hp5412(b) switch is having thousands of discards at the port to the
>>>   CS system
>>> o Enabling flow control on all the switches on the mesh almost
>>>   completely eliminates the discards and increases read performance, but
>>>   hurts write performance
>>> o Reversing the flow above does not have the same performance problems
>>> o Reversing the flow above does not cause discards on hp5412(a)
>>>
>>> #---- B
>>> NA -10g-> hp5412(a) -10g mesh-> hp5412(b) -10g-> hp5800 -1g-> CS
>>>
>>> o The above scenario has no performance issues.
>>> o Still seeing discardson hp5412(b) due to other traffic on the switch
>>>
>>> #---- C
>>> NA -10g-> hp5412(a) -1g-> CS
>>> NA -10g-> hp5412(a) -1g-> hp2500 -1g-> CS
>>>
>>> o The above scenario works fine.
>>> o The hp5412(a) is not seeing the discards that hp5412(b) does.
>>>
>>> Any ideas on how to go about trouble shooting this?
>>>
>>> I am not looking for free answers to this problem here, I would be glad
>>> to
>>> talk to someone about doing some network consulting.  Also any pointers
>>> to
>>> a networking consultant/guru would be greatly appreciated.
>>>
>>> Thanks.
>>> -MichaelC
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> -MichaelC
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