NICs:  TOE (TCP Offload Engine) vs TCO (TCP Checksum Offload) in an iSCSI environment

Posted on 2011-05-02
Last Modified: 2012-05-11
I have a pair of HP DL360 G5's that I need to connect to a Dell Equallogic PS4000 SAN.  I am looking for a compatible NIC to put into these servers to allow for the most efficient means of communication between the SERVERS and the SAN.  HP has pointed me in the direction of HP NC364T, which is a 4 port half height (required in this server) card that supports TCO.  To date, every card that I have ever connected to an Equallogic SAN with has had TOE, not TCO.  HP support is telling me that this should be the same for this particular application.

Can anyone tell me if TCO is sufficient for an iSCSI environment to take the TCP overhead off of the processor / OS the way that TOE does?  We have tried my favorite cards, the Broadcom netExtreme II 5709, and this did not seem to work well with the HP hardware (we usually use them in Dell).

Any insight is appreciated.  Thanks.
Question by:jkeegan123
    LVL 55

    Accepted Solution

    TOE is a generic term that means it offloads some TCP/IP work, TCO is therefore part of what some TOE cards do. The  NC364T isn't equivalent to the Broadcom 5709 though since it doesn't do iSCSI offload. The 5709 is what HP call Multifunction server adapter, they brand it as NC382, you get them on the G6 motherboards. I guess any HP multifunction adapter would do such as NC380T but it's only 2 ports.

    Not surprised you have problem with the generic cards in HP servers since HP's drivers are tweaked a bit.
    LVL 41

    Expert Comment

    Are you actually running into CPU problems using your existing cards? I run iSCSI on my built-in NICs and basic Intel gigabit server NICs and have no problem with CPU utilization for either the host or VM when connecting to EqualLogic. I don't do any type of non-default offloading. I may eventually turn on jumbo frames. I feel that for most applications worrying about offloading leads to a less reliable system and wastes lots of time troubleshooting.
    LVL 5

    Author Comment

    We are getting ready to put in a 2 node Exchange 2007 cluster on multiple Hyper-V VMs that will live on Equallogic iSCSI LUNs, and I'm just following all whitepaper recommendations as we setup.  The organization that we are doing it for will have over 1000 Exchange users, so I'm just trying to get things as fast as possible.

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