I just purchased a CRS504-4XQ switch upgraded to 7.20.6 to connect seven PCs that all have Mellanox ConnectX5 cards (running current FW 16.35.8002). There are three that are connected via copper Mellanox cables at 100Gb and they work great. They can run RDMA all day configured at 100Gb without issue.
I intend on having the other four PCs connect at 25Gb via a Mikrotik XQ+BC00003-XS+ break-out cable which I purchased with the switch. But of course those are SFP connectors at 25Gb which then need to go into the ConnectX5’s QSFP connector.
Alas, I went for something cheaper than Mikrotik’s XQ+CM0000-XS converters so I bought four 10Gtek WADQS-28 adapters (https://www.10gtek.com/products/QSA-381.html) to transition from SFP connector on pigtail to the ConnectX5 QSFP. They sure look to me like they do the same thing.
To cut to the chase, it’s not working. Before I get too far into all the settings I’ve tried in WinBox to set each channel to 25Gb, let me just ask: Is this supposed to work? If so then I will go buy a XQ+CM0000-XS converter to make sure it’s not the cheaper converters before I continue mucking about with the config.
I suspect that the answer is “no, those SFP to QSFP adapters are for going into the switch only and it’s not supported to go from an SFP connector off of the pigtail into a QSFP connector in the NIC”. Hope that isn’t the answer but figured I’d ask before investing a couple hundred dollars in the Mikrotik adapters.
With the cables and cable adapter cost escalating, I probably should have just spent the bucks for the CRS520-4XS-16XQ to go 100Gb across the board.
So I won’t post any WinBox or ConnectX configuration settings I’ve tried until someone says “yes in theory that should work”.
Thanks for the help.