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A Comparison of two Gigabit SAN/LAN technologies: Scalable Coherent Interface versus Myrinet

Several commercial Gigabit interconnect technologies are currently emerging due to the results of the intensive research with the NSF Gigabit Networking testbeds. A fair comparison of these new, but different network technologies needs a common denominator as a basis. To characterize networking performance, we propose to carry out a comparison at three different levels: (1) simple remote load/store operations, (2) message passing libraries and (3) standard IP over LAN networking. Our comparison includes the two Gigabit Interconnects for the PCI bus that are targeted at clusters of PCs, Myrinet and Dophin SCI. Just for a reference the interconnect technology of the SGI/Cray T3D is evaluated with the same benchmarks. After a description of the hardware in three different network interfaces, we take a closer look at the communication operations and determine the “native” and “alternate” modes of operation of the different technologies. For a direct comparison we present uniform throughput measurements for all three architectures at all levels of communication services. Myrinet and the Cray T3D can sustain a full Gigabit/s transfer rate for large transfers of contiguous blocks. The Dolphin SCI cards peak at somewhat more than half a Gigabit/s despite the faster raw hardware speed. The two PCI based system can not sustain their good performance when the communication involves non contiguous data, when the message passing semantics require buffering in main memory or when an IP over LAN emulation is used. Given the low cost of these interconnect boards, their performance close to a Gigabit is remarkable, but due to the afore mentioned limitations we expect that any Cluster of PCs built with those PCI card interconnects will get into some difficulties with applications that require complex, dense communication patterns or support for standardized high level networkin software. Keywords—SCI Networks, Myrinet Networks, Gigabit Networking, Network Interface Architectures, Shared Memory, Message Passing, Remote Loads/Stores, Performance Evaluation, MPI, PVM and TCP/IP.