HI Petter,
some questions:
"The communication from the ConnectX3 Pro EN 10G card to the Mellanox SX1012 is working fine, "
Not sure what it means, which cable is used in the above scnario
'but the Mellanox cable
40G-10G Hybrid cables with SFP+ - QSFP is not connecting."
This type of cable requires configuring the SX1012 switch port with the below command(s):
To use all 4 SFP+ ends of the cable:
switch(config)# interface ethernet 1/x module-type qsfp-split-4 force
To use all 2 SFP+ ends of the cable:
switch(config)# interface ethernet 1/x module-type qsfp-split-2 force
It's explained in the MLNX-OS UM section 5.1.1 (configuration example - 5.1.1.1)
The SX1012 supports to have all of it's 12 ports to be split.