Fibre channel storage is great because it mostly "just works". You give provision storage, assign it to the WWPNs, rescan the adapters, and boom, your luns are presented. There isn't a lot of configuration in the GUI and honestly it can be hard to detect link speed or even if a link is up. In the storage adapter tab you can see if a path is down but how do you detect the link speed?
I really don't intend to constantly write about ESXCLI or PowerCLI but those tools are lesser known to the average administrator and really help with troubleshooting.
To check your links either SSH to a host or use the VMA (expect an article about this soon!) to issue this command
esxcli storage san fc list
This command will return a good amount of information on your Fibre Channel HBAs
Let's suppose one of your adapters negotiated too low and you needed to try to renegotiate with your storage switch. How would you cause vmhba2 to renegotiate with the switch?
esxcli storage san fc reset -A vmhba2
That's all it takes