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I'm currently looking into an cheap InfiniBand solution and it seems like used 20 Gigabit/s host cards and switches are rather cheap to get but I'm getting really confused when it comes to cables as the prices are differing a lot and their tech description differs as well (if they even have any, many that I found just have a part number and the length).

I couldn't find any ressources that explain the diffrences (if there are any). I found cables that are supposed to connect to SAS/S-ATA which sounded very weird to me and it seems that there is some sort of quality difference.

So, what do I need to look for if I want a cable that would connect a host card and switch that support 20Gbit/s (both card and switch that I looked into a little closer have a "4x DDR" spec but I'm not exactly sure what that tells me, DDR as in DDR memory?).

Some clarity would be much appreciated.

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Following two sections are direct quote from Wikipedia

Effective unidirectional theoretical throughput (actual data rate, not signaling rate)

         SDR       DDR       QDR     FDR-10           FDR        EDR
 1X  2 Gbit/s  4 Gbit/s  8 Gbit/s  10 Gbit/s  13.64 Gbit/s  25 Gbit/s
 4X  8 Gbit/s 16 Gbit/s 32 Gbit/s  40 Gbit/s  54.54 Gbit/s 100 Gbit/s
12X 24 Gbit/s 48 Gbit/s 96 Gbit/s 120 Gbit/s 163.64 Gbit/s 300 Gbit/s

Physical Interconnection

InfiniBand uses copper CX4 cable for SDR and DDR rates — also commonly used to connect SAS (Serial Attached SCSI) HBAs to external (SAS) disk arrays. With SAS, this is known as an SFF-8470 connector, and is referred to as an "InfiniBand-style" Connector. The latest connectors used with QDR and FDR are QSFP (Quad SFP) and can be copper or fiber, depending on the length required.

So it seems SAS cable is acceptable in some situation.

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Thanks, thats good to know. So CX4 is the cable type used for any cooper based Infiniband product and does not mean it uses 4 connections? – Professor Sparkles Jan 21 '13 at 22:13
That may be in relation to SAS, which is essentially 4 SATA 3/6gbps connections in a single cable. – Justin Jan 21 '13 at 22:38
I see so as long as the connector fits I don't have any complication with using a cable that is certified as a SAS InfiniBand cable? – Professor Sparkles Jan 22 '13 at 15:27

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