Hi Bud,
Assuming you're using OFED 2.4 - Can you copy paste dmesg output when the low lever driver loads (mlx4_core) ? and you can also try optimizing the flow steering mode - just create a mlnx.conf file under /etc/modprobe.d/ and put the following line :
options mlx4_core log_num_mgm_entry_size=-7
Then reload the driver.
FC = Flow control, assuming it is enabled on the NIC (ethtool -a ethX) it is needed also to be enabled on every switch port on your Arista.
Regards,
Erez