On Thursday 18 January 2007 09:52, Robin Humble wrote: ... > is ~10Gbit the best I can expect from 4x DDR IB with MPI? > some docs @HP suggest up to 16Gbit (data rate) should be possible, and > I've heard that 13 or 14 has been achieved before. but those might be > verbs numbers, or maybe horsepower >> 4 cores of 2.66GHz core2 is > required?
The 16 Gbit/s number is the theoretical peak, IB is coded 8/10 so out of the 20 Gbit/s 16 is what you get. On SDR this number is (of course) 8 Gbit/s achievable (which is ~1000 MB/s) and I've seen well above 900 on MPI (this on 8x PCIe, 2x margin). The same setup on 4x PCIe stops at a bit over 700 MB/s (for a certain PCIe chipset) so it makes some sense that an IB 4x DDR on 8x PICe would be limited to about 1500 MB/s (on that platform). All this ignoring possible MPI bottle necks above 900 MB/s and assuming the IB fabric can reach 95%+ of peak on DDR as it does on SDR... /Peter
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