Last week, I bought two QLogic Fibre Channel adapters QLE2462 to start learning about Storage Area Network. I put it to two Dell PowerEdge T110 Servers and connected them using two LC-LC duplex cables. Servers are running Ubuntu 14.04 LTS. I would like to configure first as FC target and second as FC initiator. On target I installed targetcli, I created targets, luns and ACLs, initiator sees it so everything seems to be fine. But there is one problem: transmit and receive speeds between the adapters are very random.
For example: after a period with good transfers (400MB/s transmit or 400MB/s receive or 350MB/s and 350MB/s simultaneous transmit and receive) there is a period with very slow transfers (in range from 1MB/s to 200MB/s) or LUNs are inaccessible. LUNs created on target server are RAM disks.
I have found that moving connectors at ends of cables have great impact on speed, for example when I plug a connector to port on adapter to the end (there is a "click" sound) there are slow transfers and when I gently draw it out transfers are good. This is not a solution because after some time the situation is reversed and transfers are slow again so I must "correct" connectors and it works good again.
Cables are 1 meter long. I suspect that adapters or cables have failed, but I do not have opportunity to check it in another environment. Maybe I did something wrong, my SAN knowledge in minimal... What could be the reason for this unstable behaviour?