We have a number of Chelsio 10GBE ethernet NICs, model N310E and N320E with driver v184.108.40.206. In our experience, if the Linux Kernel option IRQPOLL is set, the cards will not sustain intensive use. While one can ping all one likes, continuous NFS traffic, such as that produced by iozone, will cause the mount to hang until a reboot. IRQPOLL is not set by default in RedHat or Ubuntu but we observed boot messages suggesting it be enabled in some of our systems, and did so to our disadvantage.
The Chelsio cards onboard firmware for dhcp booting checks the Vendor ID field of a DAC and refuses to work with non-Chelsio brand DACs. The Linux and FreeBSD drivers do not check, and will work with other brands of direct attach cables if the computer is booted without use of dhcp.
April 12, 2013