QSA28 (QSFP28 to SFP28) Adapters on Mellanox ConnectX-4?

[jmsq]

Hi all,

In my journey from 10/40gbe on ConnectX-3 NICs to 25/100gbe on ConnectX-4 (and Lx) NICs, I've discovered that I can't manage to get any CX4 or CX4Lx QSFP28 cards to link up with QSA28 adapters to SFP28 optics or DACs, either with the MAM1Q00A-QSA28 or generic equivalents. I've used QSA non-28 (MAM1Q00A-QSA) adapters extensively in the past on CX3 cards with zero issues regardless of SFP+ optics/DACs plugged into them, and these continue to work fine on the CX4 cards, but I get nothing with QSA28. At first I thought it might be an FEC issue, but all the workarounds to make that work with standard CX4 SFP28 cards have no effect for the QSFP28 cards with the adapters. Is there a known compatibility issue here? Is CX4 super picky about QSA28 adapters and I ended up with non-genuine Mellanox ones from ebay? Any suggestions would be helpful.

Thanks,
JM

 

[nexox]

I have had some issues with my ConnectX4 and QSA28 adapters, several 10G DACs worked, none of my 10GBaseT transceivers did, one 10G AOC does work but a 25G AOC doesn't. It doesn't seem to be brand locking or anything, and all that stuff works on my SFP28 ConnectX 4 Lx, I really don't know what is going on.

 

[jabuzzard]

As far as I can make out when you plug in a QSFP to SFP adaptor into a NIC or switch they have zero idea that it exists. No tool that I have tried shows anything. It's not till you put the SFP module in that the NIC or switch shows anything for that port.

Having dismantled a QSFP+ to SFP+ module as far as I can tell, it passes through the 2-wire serial interface lines to the SFP and has some circuitry to generate the QSFP module present signal from the SFP module absent signal along with some capacitors that look like they are to deal with voltage transients if you hot plug the SFP module. The TX1/RX1 on the QSFP are passed through to the TX/RX on the SFP

As such there is as far as I can tell no difference between a QSFP+ to SFP+ module and a QSFP28 to SFP28 module. Which sort of stands to reason.

I would like to break out some 200Gbps ports to 4x50Gbps but while I can get SFP56 SR modules there are no cards I can find that support them and nobody does a QSFP56 to SFP56 module, hence why I have been dismantling an adaptor. We are probably going to get a single SFP56 SR module to experiment with.

Note I do have a 845970-B21 from HPE in one of their rebadged SN3700M Mellanox switches with an fs.com 25GBaseBX module. The other end is a Dell with a ConnectX4 with a couple of SFP28 ports and the corresponding fs.com 25GBaseBX module.