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Author Topic: Any miners "diasychaining" PCIE ribbon extenders?  (Read 1738 times)
rhubear
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November 20, 2011, 05:34:24 PM
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Hi miners,

I've recently got into bitcoin mining, and this weekend read in this forum about pcie extender cables.  It took me a little while to understand a little how to apply these extenders (boggled my mind that this was possible!).

One thing that I'm not clear about yet is whether or not miners use more than 1 extender (from Cablesaurus or your own fav vendor) to relocate a vid card somewhere else in your mining box (if you're using a box!).  The length of extenders sold by Cablesaurus is only 19cm, not very long at all.  Even for me to relocate a vid card from a pcie1 slot to a front bay in my Thermaltake Armor box would prob need 2 or 3 extenders.  I don't want a large vid card flopping around my case! 

How do you guys use extenders?  Will extenders work if daisychained to get the length?  What is the max length of extender cable that has worked for you guys?

Cheers/tnx for any info!

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rhubear
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November 20, 2011, 11:36:42 PM
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Well, no-one answering here, but I got a semi definitive answer from Cablesaurus, so I'll try out what I have in mind.
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November 20, 2011, 11:47:37 PM
 #3

I have seen a picture with two extenders daisychained. People were surprised, but supposedly it worked. YMMV

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November 22, 2011, 01:31:05 AM
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I too have only seen pictures, but the rig in question was working... I would have to answer a tentative 'yes'.

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November 22, 2011, 02:07:06 AM
 #5

Hi guys, two of you have been kind enough to reply.  I thought I would share what Cablesaurus shared with me.... 

The guy said
1)  milage would depend on the motherboard, he couldn't specify which MB.
2)  Using a molex powered extender as the one plugging into the card would give the best chance of it working.
3)  he had only seen 2 cables daisy chained together but thought that more chained together should work.

So thats what I know for the time being.  Will let you guys know how I get on!
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November 22, 2011, 03:01:38 AM
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I would have to note, that you would quickly rack up ridiculous latency.

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November 22, 2011, 06:39:48 AM
 #7

latency shouldn't be too bad though, because the amount of data transferred to/from the videocard is not very high, as far as I know.

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November 22, 2011, 09:26:39 AM
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Latency has nothing to do with bandwidth or the amount of bandwidth used. It has to do with the propagation delay in the signal line, since signals travel about 1/10th the speed of light in copper, making the distance a considerable factor.

PCIe is designed for a maximum signal trace of 50cm (that includes the PCB traces in the motherboard and cards). Timing issues can arise beyond this. In addition, if you have external connections like the PCIe extender, each one can cause signal losses by increased RF susceptibility, cable attenuation, and signal reflection (and unterminated 'antenna' losses in the connector) at each medium change.

"PCI Express is optimized for a 4 layer FR4 [Dielectric], supporting up to 20 inch distances between devices. The actual distance between IC's depend on the number of via's. The differential trace impedance is defined as 100 ohms + 15%. Each trace pair should have a matched trace length of + 5 mils. How ever pair-to-pair trace length matching is not required. Each signal pair is capacitive coupled at the receiver. Do not stager the capacitors for each signal pair, they should reside next to each other. Jitter in the PCI Express Interface: PCI Express specifies a maximum output jitter of 120ps for the Serializer and a minimum input jitter tolerance of 240ps for the De-serializer. The UI [Unit Interval] is the bit time = 400ps, Phase Jitter most important. The UI of 400ps is 1/[2.5Gbps]. The Bit Error Rate [BER] is defined as 1x10-12." (looks like this engineer can't spell...)

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November 22, 2011, 09:25:44 PM
 #9

I hadn't even thought about possible RF interference. Nice call there.

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DeathAndTaxes
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November 22, 2011, 09:28:52 PM
 #10

If you need more than 1 extender you are doing it wrong. 

Try rethinking the problem. 
legolouman
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November 22, 2011, 10:33:55 PM
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If you need more than 1 extender you are doing it wrong. 

Try rethinking the problem. 

I think that with two, you can REALLY increase the effectiveness of your mining, and heat dissipation. On the other hand, you have a point.

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January 19, 2012, 03:53:57 AM
 #12

Now that it's been a couple months, I'm curious how happy the OP was with his experiment in using multiple extenders to give his GPUs more breathing room.  Did it work well, or did you need to rethink the problem?  Thanks.
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