SDR

10Gbps connection that uses a CX4 connector. Very old equipment, but very cheap!

DDR

DDR Infiniband is the second iteration of the standard. It operates at 20Gbps (16Gbps after throughput loss due to encoding) and uses either CX-4 or QSFP. Most DDR devices I’ve seen use CX-4. Personal opinion: CX-4 is such an ugly connector. Who designed that? Topspin switches are cheap and cool for learning Infiniband, and most of them operate on this standard.

QDR

Switches that operate to this standard usually provide connections rated at a throughput of 40Gbps (32Gbps after encoding loss) and a latency significantly lower than Ethernet’s. The connection type for most 40Gb Infiniband is (QSFP+). A lot of newer Mellanox switches offer something they call VPI, which allows configuration on a port by port basis as to which protocol you’d like to use (Ethernet or Infiniband). I personally like this feature, because it allows for flexibility within my lab.

Before they were bought out by 100 different companies, there was a company called Voltaire that made QDR switches. If you’re looking for the cheapest QDR switch you can find, that’s probably a route worth exploring.

FDR-10/FDR

F stands for FAST. I run an SX6018 at home. It draws about 40W under a modest load and is the quietest IB switch I’ve ever owned.