Chelsio T5 vs. T6 SFP+ Adapters



  • Hi all,

    I'm planning to add an PCI Express SFP+ network add-on card to my Supermicro 1U server and have started to look at Chelsio cards since they are well supported in FreeBSD/pfSense.  I had just a couple questions for those of you know who more about these cards before I got out and make a purchase:

    1. Is there a good reason to go with a T6 card vs. a T5 card (previous generation)?  I see that the T6 supports crypto offloading now as well (e.g. TLS/SSL, IPSec, etc.), but from what I can tell this is not yet supported in FreeBSD (I did see support for Linux though).  Is there any other reason why it make more sense to go with a T6 based card?  The price difference between the T5 and T6 isn't all that much so that is why I'm curious.

    2)  Is there a good reason to go with a regular card versus the memory free server offload ("SO") card instead (for example, the T520-CR vs. T520-SO-CR)?  From what I can see the regular cards support more connections for TCP offloading (~32 for the SO-CR and ~32000 for the regular CR).  Wouldn't this be advantageous to have for pfSense?  Or are the benefits not really apparent until one regularly pushes multiple gigabits/second through their network?

    Thanks in advance for your help, I really appreciate it.



  • I'm not sure in this case, but in many cases the hardware offloading does not apply well or at all to a router/firewall because it doesn't terminate the connection. For example, TSO and GSO can cause issues with packet pacing and buffer bloat. Great for throughput where you're CPU bound. I'm not sure how the TCP offloading works to know if it matters at all for a stateful firewall.



  • @Harvy66:

    I'm not sure in this case, but in many cases the hardware offloading does not apply well or at all to a router/firewall because it doesn't terminate the connection. For example, TSO and GSO can cause issues with packet pacing and buffer bloat. Great for throughput where you're CPU bound. I'm not sure how the TCP offloading works to know if it matters at all for a stateful firewall.

    Thanks Harvy - that is good info to know.  Beyond what you said, I'm not sure that in my use case the additional benefits are worth justifying the incremental cost of the regular version of the card.  Thanks again.



  • Well, I decided to go with the previous generation memory free server offload card, i.e. the Chelsio T520-SO-CR, since I found a pretty good deal on it.  Will follow up here with some impressions once everything is installed and up and running.