@DarkyToo - I was just reading your tutorial, and I noticed that the speeds you listed in your tutorial were/are wrong.
You stated:
SDR: Single Data Rate, this is referred to as
10mb, when it’s really only 8. This is the cheapest speed to start with Infiniband, switches run about $200. These use a CX4 Connector
DDR: Double Data Rate, this is referred to as
20mb when it’s really only 16. DDR switches start around $400-$500. DDR Connections still use a CX4 Connector
QDR: Quad Data Rate, this is referred to as
40mb, when it’s really only 32. QDR switches start around $1000. For QDR and above connections, the use a QSFP Connector.
FDR & EDR: these run at
50mb and
100mb. These are beyond the scope of this article.
I believe you meant to say "
10Gbps" (instead of 10mb), and meant to say "
20Gbps" (instead of 20mb), and meant to say "
40Gbps" (instead of 40mb). Also I believe FDR and EDR are 56Gbps and 100Gbps respectively.
See here:
InfiniBand - Wikipedia, the free encyclopedia
SDR, DDR, and QDR use 8b/10b encoding, so you'll lose about 20% of the bandwidth due to the encoding. So yes, a 10Gbps link (4x SDR) would only be about 8Gbps of throughput and a 20Gbps link (4x DDR) would only be about 16Gbps of throughput. A 40Gbps link (4x QDR) would only be about 32Gbps of throughput.
FDR-10, FDR and EDR use 64b/66b encoding, so you're only losing about 3% of the bandwidth due to the encoding (instead of 20% with 8b/10b). So a FDR-10 40Gbps link (4x FDR-10 @1.25GB/s per link = 5GB/s = 40Gbps theoretical) would get about 38.788Gbps of throughput (with 64b/66b encoding). A FDR (4x FDR/FDR-14 @ 1.71GB/s per link = 6.84GB/s = 54.72Gbps theoretical) would get about 53.062Gbps of throughput (with 64b/66b encoding). An EDR (4x EDR @ 3.13GB/s per link = 12.52GB/s = 100.16Gbps theoretical) would get about 97.125Gbps of throughput (with 64b/66b encoding).
Keep in mind, that is just based on data rates, and none of these calculations take into account the additional physical layer overhead requirements for common characters or protocol requirements (such as StartOfFrame and EndOfFrame, etc.)
Would love to see you update your page/tutorial, and I hope this helps...
Thanks,
Mark