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Viewing virtual channel throughput

  • 1.  Viewing virtual channel throughput

    Posted 04-04-2016 06:58 AM

    Does anyone know a way of viewing throughput per virtual channel?  We're trying to test SAN QOS, and it'd be nice to be able to see a rough view at least that it's doing what we expect.  Thanks.


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    #qos


  • 2.  Re: Viewing virtual channel throughput

    Posted 04-04-2016 08:13 AM


  • 3.  Re: Viewing virtual channel throughput

    Posted 04-04-2016 08:32 AM

    I've never known portperfshow to show anything more than the throughput for a port.  What we're looking for is the throughput for each virtual channel.  Something like the zero credit counter in a portstatsshow.


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  • 4.  Re: Viewing virtual channel throughput

    Posted 04-04-2016 08:59 AM

    -->>Something like the zero credit counter in a portstatsshow.

     

    what are the value of "portcfgeportcredit --show"

     

     

     


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  • 5.  Re: Viewing virtual channel throughput

    Posted 04-04-2016 09:02 AM

    "E-Port Credit Configuration is not Enabled"


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  • 6.  Re: Viewing virtual channel throughput

    Posted 04-04-2016 09:08 AM

    If the problem is caused due a bottleneck, I would suggest to enable and set the buffer credit value.

     

     


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  • 7.  Re: Viewing virtual channel throughput

    Posted 04-04-2016 09:14 AM

    There is no problem.  I'm wondering if anyone knows how to view the throughput/traffic down a virtual channel or down a particular QOS group.

     

    It might be that I'm missing the point.  My understanding is that when you use QOS, if a port becomes congested, the high priority traffic will get to go first.  Or is it purely a buffer thing, allocating more buffers to high priority traffic, but then if a port is at 99% utilisation, traffic in any VC will get through?


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  • 8.  Re: Viewing virtual channel throughput

    Posted 04-04-2016 09:43 AM

    ->I'm wondering if anyone knows how to view the throughput/traffic down a virtual channel or down a particular QOS group.

     

    I don't know how you can view such a traffic, i was the opinio portperfshow should work.

     

    ->There is no problem. 

     

    Is problable that this is not a problem, now I'm not sure if you are looking for a solution or just how to view the traffic.

     

    ->Or is it purely a buffer thing, allocating more buffers to high priority traffic, but then if a port is at 99% utilisation, traffic in any VC will get through?

     

    if the port in question congest, ( in example if the port is set as LE, the port in question should become more Buffer allocated, but due the aoutomatic allocated buffer this will be distributed across the port's )

     

    ->My understanding is that when you use QOS, if a port becomes congested, the high priority traffic will get to go first. 

     

    the goal from portcfgeportcredit is, to assign to a affected port a required buffer.


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  • 9.  Re: Viewing virtual channel throughput

    Posted 04-05-2016 05:50 PM
    Sorry, there's no command to see the traffic per VC. In a way, you can have a look at the tim_txcrd_z counters on the port, they have a breakdown per VC. So you might see if some of the VCs are highly utilized. Note that incoming and outgoing traffic might use different VCs. Maybe the Flow part of the MAPS can give some more insight, but I didn't use it yet so I can't tell for sure.
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  • 10.  Re: Viewing virtual channel throughput

    Posted 04-06-2016 04:01 AM

    What do you mean by talking about VC throughput. It's not quite clear what do you want to measure. Physicaly you have the link and VCs are just something like queues. QOS will work only when ISL congestion occurs. Thus you will have 100% link utilization and some VCs will get more or less priority.


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  • 11.  Re: Viewing virtual channel throughput

    Posted 04-06-2016 04:23 AM

    We basically want to test QOS so that we properly understand it before implementing it on our live SAN.  The aim is that we get latency events for various reasons, and although as time goes on we add or tune different features to mitigate or eradicate different reasons for latency, a new flavour of latency always seems to pop up somewhere else. And for various reasons, we need to start protecting certain traffic from the impact of SAN latency.

     

    However in our testing, it would just be nice to be able to 'see QOS working' somehow. 

     

    Thanks to Alexey's suggestion, we've found you can create a flow using Flow Vision in a QOS class, so our current tactic is to try to use this create latency in the low priority QOS group, which shows up under the latency count in portsstatshow, but then also to run io generators on three servers in each QOS group, and hopefully see SCSI timeouts on the low priority server but no interuption on the others.  Getting latency messages is the easy bit, actually producing C3 discards seems much harder.


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  • 12.  Re: Viewing virtual channel throughput

    Posted 04-06-2016 01:41 PM

    I think you could imitate the slow drain device (SDD) by setting its port speed below the fabric value. This will lead to SDD are not being able to return credits fast enough and to credits starvation back pressure into fabric. Finaly you might see c3 discards due to timeout.


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