I believe fibre channel devices are only backwards compatible 2 speeds worth. For instance 4 Gbps ports work at 4/2/1 Gbps. I would assume your 8Gbps ports will only do 8/4/2 Gbps. Might need to check the data sheet on that particular switch.
Hi,  A customer has two 8 Gbps Connectrix DS300-B. We need fix speed one port to 1 Gbit/sec for WDM link.  When we did it (portcfgspeed portnumber,1) it showed the status port like Mod_Inv. We tried the same with a 4 Gbps SFP and it was the same. We connected one server FC port to WDM link, and other site switch showed the server WWN, so the WDM link works.  I can't merge the inter-site switches becasue I can't fix speed one port to 1 Gbit/sec in 8 Gbps Connectrix DS300-B.  Anybody can help us?  Thank you.
Fix port speed to 1 Gbit/sec