Facing issue with our 10G connectivity, we have this Extreme Networks Summit X670 switch. Connected FAS3140 with Data ONTAP version is 8.0.2P3 7-Mode to the switch and host is Windows 2012 R2. Currently the write speed is 40 MB/s and read speed is in Kbs. We have Hitach and EMC storage and those are giving good write speed, around 500 MB/s.
For your reference I am attaching few command outputs that may help in analysing the issue.
Have you already checked "saystat -x"? Bottleneck may came from small NVRAM. FAS3140 has only 512MB NVRAM, so each controller in HA configuration can receive write data up to 128MB per Each CP. If each CP takes 3seconds, throughput is limited to 40 MB/s. CP time depends on workload and configuration, but 3 seconds is not so bad in common environment - well-planned RAID with fast SAS disks and/or external cache may be sometimes required for better performance in this generation.