I have a bunch of computer with onboard Mellanox ConnectX-2 QDR Infiniband 40Gbps Controllers. They have QSFP connectors.

I have a switch with 24 4x CX4 DDR connectors.

If I buy QSFP to CX4 cables, will the QDR controllers on the computers be able to downscale to DDR, and be able to communicate with (through) the switch?

1 Answer 1


Infiniband should be smart enough to negotiate a compatible data rate; in your case, since your switch is a DDR switch, your IB network will run at DDR rates.

  • Well, I have alot banking on this, so I'd like more than a "should". But thank you for your answer. I'll try to give mellanox a call, and leave this thread in case anyone else can answer. Aug 31, 2010 at 19:47
  • Update: I called mellanox and they verified that QDR can downscale to DDR. Success :D now all I need are QSFP to CX4 cables. Aug 31, 2010 at 22:23
  • 1
    Just another update, I got the IB working in fedora using the OFED package from the OFED site. Nov 10, 2010 at 16:46

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