Nexus 5k Fibre Channel speed issue

[RyanT90]

 I have a FC link on two Nexus 5000s hard set to 4gig but the speed seems limited to approx 300 Mbps. Any obvious reasons?

[Rick1776]

Can you send the configuration for those interfaces? Also are you running true Fibre Channel Switching or NPV/NPIV.

[RyanT90]

Fibre channel switching i believe

interface fc1/35
  switchport speed 4000

interface fc1/35
  switchport description ***PUL_EPR_011***
  no shutdown

vsan database

So after speaking with the customer it would appear the link is over 10km and they have no buffer credit setting in place. I'm thinking this could be a cause?

  vsan 400 interface fc1/35

[Rick1776]

For starters I would match the configuration on each side. So for instance.

interface fc1/35
switchport description ***xxxxx***
switchport speed 4000
no shut

interface fc1/35
switchport description ***PUL_EPR_011***
switchport speed 4000
no shut

vsan database
vsan 400 int fc1/35

The buffer to buffer credits wouldn't help if you are experiencing latency on the link.

[calopez2]

Can you provide transceiver details to verify the SFP type currently installed? on both ends.

[Rick1776]

Hmm, I was doing some research and it looks like you are correct to look at the buffer credits.

Also looks like there is a distance limitation so for 10Km it states in the link below that 800KM has a bandwidth of 1G.

Please see the link below.
https://blogs.cisco.com/datacenter/storage-distance-by-protocol-part-iii-fibre-channel