Monday, September 15, 2014

Remote Direct Memory Access - RoCE versus iWARP

Remote Direct Memory Access (RDMA) is the technology that that allows server-to-server data communication to go directly to the user space (aka application) memory without any CPU involvement. RDMA technology delivers faster performance for large data transfers while reducing CPU utilization or overhead. It is a technology used in many applications segments – database, storage, cloud and of course HPC. All of the MPIs include support for RDMA for the rendezvous protocol.
There are three communications standards for RDMA – InfiniBand (the de-facto solution for HPC), RoCE and iWARP. The latter two are over Ethernet. RoCE has being standardized by the IBTA organization, and iWARP by the IETF.
iWARP solutions are being sold by Intel (due to the acquisition of NetEffect) and Chelsio. RoCE solutions are being sold by Mellanox, Emulex and others. The major issues of iWARP are performance and scalability. With iWARP, the data needs to pass through multiple protocols before it can hit the wire and therefore the performance iWARP delivers is not in par with RoCE (not to mention InfiniBand). The major RoCE limitation was with support over layer 3, but this has been solved with the new specification that is about to be released for RoCE v2.
Last week Intel announced their new Ethernet NICs (“Fortville”). No iWARP support is listed for these new NICs, and this leaves Intel without RDMA capability for their Ethernet NICs. Seems that the iWARP camp is shrinking… well…  there is a RoCE reason for it…

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