Do the McData datasources ever inventory successfully?
If yes - what is the ping time between OCI and them? It may be that WAN issues are a problem. It may mean that deploying a Remote Acquisition Unit may help, or it might be possible to bump up retries within the datasource.
consult the support matrix, and ensure your firmware is supported. Some firmware fundamentally have wonky SNMP stacks, and are unsupportable
Use the snmpwalk.exe to validate that your OCI server can communicate via SNMP to the McData switch with the same community string you are using.
Re: Alternative datasource type for McData switches
I would use KB 2014313 to increase the retries before increasing the timeout. I don't think there is a high likelihood of a SNMP UDP frame arriving > 1 second after it was sent - it is going to come within a second, or it isn't going to come after all.
Calculate your datasource success % for a 7 day period, then try setting the retries to 3, and then calculate the resulting success %