backward compatibility FDR vs DDR

I’m end user of big IB infrastructure and we are trying to gain new experiences in this field in our group. We have access to old DDR switch and we want to use it with some new FDR IB (or EDR) cards (ConnectX® series VPI QSFP28). My question is : Is it possible to use FDR(EDR) card with DDR switch on DDR speed with QSFP28 (FDR/EDR) cable (in future we want to replace switch but first we want to gain some experiences). Is it better copper or optical cable? Thanks for your reply.

Hi, FDR to DDR is not supported. It is possible you may get link UP between a DDR and FDR device, but its not something tested/validated, so therefore is unsupported.

QDR to DDR would work, FDR to QDR would work, as would EDR to FDR,but EDR to DDR will not work, and FDR to DDR likely won’t work.