statport will show you load on FC ports, this will enable you to see which port is loaded more than the others.
statvlun -hostsum (host summary), this might be easier way to indication which host is top polluter. Will not tell you on what port that host is creating traffic, but you will use the combined information to identify where round-robin is missing.
statvlun is most likely what you are looking for : it displays DETAILED breakdown of "vv per host per port" communication statistics, but be prepared to get some LENGHTY output which is not easy to process. Every single LUN, accessed by every single host by every single path...
You can shrink down that output by limiting only the "offending port" you identified by using "ports" - ie. if you know you have heavy traffic on x:y:1, you don't need to display anything else. Use -ports 1 for statvlun and it will only display ALL ports X:Y:1
Example of my unbalanced configuration :
http://imageshost.eu/images/2017/11/15/3par.pngby using statport, I caught the problem to be on port 3:5:2 - this is not displayed here. By using statvlun with "-ports 3" I demonstrate there is not too much traffic on X:Y:
3 ports. And there is brutal difference with output of command where I used "-ports 2" showing tremendous traffic on ports X:Y:
2Because I used HOSTSUM switch, it's very very easy to instantly identify host (actually two or three) being responsible for majority of traffic.
Apologies, I had to scramble the names of hosts due to company security policies.
As you see on screenshot, out of total 563117 kB/s two hosts (name ending with 02 and 06) were responsible for 264227 + 165724 = 429951 kB/s ; that is 76% of all traffic was generated by two hosts only. If I add the third largest consumer, that would be additional 80686 kB/s which is pushing me to 90%... three hosts responsible for 90% of all traffic on single port !
Sure, this is short-term data only, but you get the idea...