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Hello,

I'm currently building a gaming pc for myself. and I have an Sabertooth 990FX with FX8150 processor.

I manage to get 3pcs. of Asus HD 6970 DCU II GPU Cards, and in order to install the 3 cards at the same time into my motherboard I need to use PCI-e Extenders that I'm aware you all know about. The problem is, everytime I attach the pci-e extender in slot 1, the card is ok. but when I attache the extender at slot 3 and slot 4, the problem starts, the card loses it's performance and giving me bsod. I'm not sure if its because of lacking sustaining power for each slot? I hope you can help me. I badly need your help guys. Thanks

and sorry for my bad english.

Three issues with that setup that I can think of. 

1.  You'll need a 1000W power supply.

2.  Your PCI-e slots need to be rated at 16x or 8x for all three of those cards, or you will have issues.

3.  Tri-fire (3 cards, two crossfire bridges) is tricky to set up, I tried it with 5870s and got blackscreen crashes or little improvement in most games, the drivers just didn't support it very well.  May be improved with the 6XXX series.  Two overclocked 6870s will deliver a nearly-perfect gaming experience on all games currently available, unless you've got a 30" Eyefinity or 3D setup. $$$$$$$$$$$$

4.  PCI-E power delivery shouldn't be an issue with three cards if your board has the slots.  If your power supply is big enough and your PCI-E slots are all 8x or greater, try removing and re-installing your video drivers with Catalyst Install Manager, re-booting after each.

Hope this helps.

Thanks for the info.

Im using a corsair AX 1200W PSU, my pci-e slots are rated at 16x, 8x, 8x when installed with 3 gpus.

I'm just having issues when I'm using the pci-e extenders attached at slot 3 and 4. but when attached to slot 1 alone, all is good.

But my setup needs to used 3 extenders.

Heya,

There could be a number of issues, some of which have already been covered:
- Power supply, you've said it's not this but be aware that a lot of PSUs are rated at X,XXX W but achieve much less than that
- PCI extenders have the potential to introduce timing issues into the equation particularly for clock-locked (ie. SLI or Crossfire/Tri-fire) deployments. If it was just a mining rig this wouldn't be an issue since I can't really see why you would need all the cards to operate on their own (as opposed to just threading the miner onto each core on the card).
- I didn't read what type of motherboard you have but there's a possibility you experience the issue in slot 2 & 3 but not 1 because the bus architecture of the board is dedicated for slot 1 (ie. the mobo manufacturer decided to provide maximum performance to a typical one card install) and then farmed out other functionalities on the same bus for slot 2 & 3 (think onboard SATA, RAID etc).

I'm not much of a hardware guy (my interest is more software related) so good luck!

Stu

This:


For gaming, extender cables are probably a bad idea Im afraid.

I see. Im using a Asus Sabertooth 990FX. pci-e is rated at 16x if 1 card is installed, 16x 16x if 2 cards are installed and 16x 8x 8x if 3 are installed.
I'm using 3x Asus HD 6970 DCU II

do you think this one can help me?

http://www.ebay.com/itm/PCIe-x16-Flexible-Extender-Cable-w-Molex-/150620070281?pt=PCC_Video_TV_Cards&hash=item2311a7e189 (http://www.ebay.com/itm/PCIe-x16-Flexible-Extender-Cable-w-Molex-/150620070281?pt=PCC_Video_TV_Cards&hash=item2311a7e189)

thanks for all the infos :)

If your problem is power delivery over the PCIe bus, it might help. But I fear thats not your problem. For timing issues, it wont change a thing.

If you plug the cards straight on to the motherboard, I assume everything works fine, or not? If you disable crossfire, and try mining, does everything work then? If the answer to both questions is yes, then nothing is gonna fix I think. Maybe shorter cables.

Pcie extenders aren't the way to go for gaming. Pcie has a trace Max distance of 60cm, and with the extenders, the cards are reaching their upper limit creating timing and latency problems. In crossfire, timing is very important.

I see. So, I can't really use this? hmmm... now that's really a bad news for me...

Looking at the Sabertooth spec sheet it explicitly has *1 on the PCIe expansion slots which references a foot note of:
"*1: When running dual graphics cards, be sure to insert the card in the first and third PCIex16 slot to get the best performance."

To me this suggests there's definitely some bus sharing going on with at least the second slot.

RE: Extender cable. Quite frankly, that ebay item looks dodgy, really really dodgy. I don't think I'd ever consider using a cable that looks like that in any PC i'd run cause I'd feel like it could catch fire.

Maybe I'm just paranoid!  :P

Stu