RDMA: Tiny Interface Produces Big Gains

Arthur Cole

Amid all the talk of enterprise fabrics, cloud computing, WAN optimization and other tricks to get data from here to there and back again, few people outside networking circles have noticed the increased use of the RDMA interface and the profound impact it is having in the enterprise.


The major benefit of using RDMA (Remote Direct Memory Access) is that it allows computing resources to access distant memory sources without involving their respective operating systems. That means data no longer needs to be copied from application memory to OS data buffers, which not only speeds up data transfers but cuts the amount of energy used by CPUs, cache systems and context switches.


RDMA is a major component of new iWARP (Internet Wide Area RDMA Protocol) technology that extends zero-copy and other RDMA features over legacy TCP environments.


Microsoft has made a major commitment to RDMA through its NetworkDirect interface designed to improve server cluster performance and to enhance HPC applications through Windows HPC Server 2008. NetEffect recently became the first Ethernet company to support NetworkDirect on its 10 GbE adapters, with early tests showing the combination can cut latency of small messages (2KB or less) to less than 6 microseconds.


Chelsio is another firm that is linking 10 GbE technology to RDMA networking. The company's Unified Wire iWARP adapters offer plug-and-play compatibility with Linux environments through support for the OpenFabrics Enterprise Distribution (OFED) stack. The company recently added support for Scali's Message Passage Interface (MPI) Connect clustering solution to enable faster communication in HPC networks.


Novel SUSE Linux users will soon have expanded access to RDMA as well when SLES 11 ships, probably early next year. Word is that it too will support OFED, which offers source drivers for both Ethernet and Infiniband implementations of RDMA.


Technologies like RDMA are proof that significant gains in enterprise connectivity aren't necessarily the fruit of major system upgrades. Sometimes that small things can have a big impact.

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