[c-nsp] EMC Centera storage problems vs nexus 5K

[John Gill]

Hello Arne,
I do not completely understand the topology - are the host and EMC 
connections all on the same N5k?  Perhaps the host is on a fabric 
extender or a different switch?  Also, do you have a monitor session 
configured?  There are scenarios where this can come into play.  It 
would be good to know the version of code in that case as well.  Sorry 
for all the questions, but I do have a hunch.

The N5k utilizes ingress queuing, so you would use "show queuing 
interface ethX/Y" on the source interface of the transfer.  You might be 
seeing "ingress discards" there if your issue is 10G to 1G 
over-subscription.

The feature we have on the Nexus 5000 to change our congestion behavior 
is to configure a class of traffic for "no-drop" and enable either 
link-level flowcontrol or priority flowcontrol (pfc) to slow down the 
source.

The issue of small files vs. big files - it clould be related to MTU or 
simply amplify the problem by letting TCP windows get large and then 
retransmissions are more costly?  What MTU setting is on the EMC and host?

Regards,
John Gill
cisco
919.392.2309

On 5/28/11 1:55 PM, Arne Larsen / Region Nordjylland wrote:
> Hi all
>
> I know it's a wild shot but I'll try anyway. I have some problems with nexus 5k and EMC Centera storage setup.
> The setup form EMC has 2 links to the 5k one 10G as primary and 1 1G as secondary.
> If the mount a nfs share and download with small files from that, they don't get more than 4-5 MB per sec in transfer. The client is on a 1G link.
> But if the download big files they can max it out. The same test with 1G works fine. I know it's no problem to overrun a 1G link with 10G.
> EMC claims that they se retransmissions, but I don't se any packet being dropped, on ether client or server interfaces.
> I know that nexus 7K has a feature that can stop sending packet to an interface that is in overload and drop the packets in the fabric, does the 5K do the same ??, and if, how or where can I se that.
> If any one has experienced something like this, I would be glad to know about it.
>
> /Arne
>
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