Jumbo Frame on Nexus 5k

[Jeremy Dubrulle]

Hi guys,

I would like to enable the jumbo frame support on my N5k for specific SCSI trafic.

I've read we can't do it per interface but only on the system itself :

policy-map type network-qos JUMBO_MTU
  class type network-qos class-default
    mtu 9216

!

system qos
  service-policy type network-qos JUMBO_MTU

But this enables jumbo frame on the whole switch. Can I identify the SCSI traffic on the policy-map so that it's applied just for the traffic I want?

And so the jumbo from other type of traffic would be processed normally ?

Thanks,

[Philip D'Ath]

What is the issue with enabling it globally?  Everything else using the standard 1500 byte MTU will work exactly the same as before.

Typically jumbo frame support is enabled globally on most switches ...

[Jeremy Dubrulle]

I've done some researches to find out if it affects performance when enabled globally. Some articles point that it should be enable just for the storage traffic. I agree it seems to don't hurt much the performances when enabled globally. Can you light me on that?

Anyway, here is the solution for the problem I had :

class-map type qos match-all iSCSI
  match protocol iscsi
  match cos 4

policy-map type network-qos JUMBO
  class type network-qos iSCSI
    mtu 9216

system qos
  service-policy type network-qos JUMBO

[Philip D'Ath]

I have never seen any impact on performance on devices not using a jumbo MTU connected to a switch with the jumbo MTU enabled globally.