Infiniband I've heard as incredibly annoying to deal with procuring as well as some other aspects of it, so lots of folks very happy to get RoCE (ethernet) working instead, even if it is a bit cumbersome.
> RDMA over Converged Ethernet (RoCE) or InfiniBand over Ethernet (IBoE)[1] is a network protocol which allows remote direct memory access (RDMA) over an Ethernet network. It does this by encapsulating an InfiniBand (IB) transport packet over Ethernet.
https://en.wikipedia.org/wiki/RDMA_over_Converged_Ethernet
Sounds very cool.