Is the MCX556M-ECAT-S25 adapter compatible with a Dell C4130 server?
The C4130 is a dual processor 1U server which has 2 half height half length x8 electrical PCIe slots which are horizontally adjacent (i.e. in line across the server, with slots fed centrally) rather than adjacent as in one slot above the other
as the adapter manual indicates is required. The adapter harness length (25 cm) would be sufficient to interconnect the cards, since their slim line SAS connectors would be very close, but a half twist in two planes would be needed in the connecting cable to make the connection. In the manual it looks like the connecting cable is a ribbon cable (which would be too inflexible) but in the product brief the connecting cable looks to be made up of separated wires which offers hope.
The C4130 is a 4 GPU server and it would be very useful to have one InfiniBand adapter serving its two PCIe root complexes.
Hi. You're right, this "Socket Direct" card is a nice capability compared to using the QPI bus between CPU sockets. However, for the C4130, I'm told Dell has no plans to qualify this. Now that Dell has released their C4140, my personal speculation is that their qualification resources will focus on the new server.
Without Dell qualification, neither Dell nor Mellanox can really support your proposed configuration, even though it might work.