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Author Topic: Multiple GPU's do I need Crossfire?  (Read 4876 times)
makko
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July 16, 2011, 06:02:21 PM
 #1

Hi Guys,

Just a quick question. If I want to run more than one ATI card for mining do I need a Crossfire board?

OR, can I just add them to any card and the mining program will use them independently?

Thanks.

Too lazy for a fancy sig.. Tongue
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macharborguy
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July 16, 2011, 06:06:47 PM
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I have two VisionTek 6870s and they are NOT set up in CrossFire (you'll get caught up in the, crosssfiiirrrraaaaaaa!!) mode.  I do have both cards plugged into my HDTV though so one of them.  I noticed that if one card wasn't hooked up to a monitor that it would not show up in GUI Miner.  You can also buy or build VGA/DVI dummy plugs to trick the card into thinking a monitor is connected.

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nafai
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July 16, 2011, 06:30:40 PM
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Crossfire lets 2 video cards communicate directly so they can better work as one. Great for gaming, totally unnecessary for bitcoin mining. Each video cards has its own set of work to do when it comes to hashing, they don't need to communicate directly. So crossfire setup is not only totally unnecessary, it can actually be counterproductive.

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makko
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July 16, 2011, 06:53:42 PM
 #4

Great stuff thanks! Smiley

Too lazy for a fancy sig.. Tongue
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July 16, 2011, 07:08:45 PM
 #5

with the 11.6b drivers you shouldnt need the dummy plug.

crossfire tends to hurt peoples hash rates.


Nice thing though, unlike gaming with bitcoin and without crossfire, you can mix and match your ati cards and dont have to use the same series. Meaning a 6990 and a 5770 can work for bitcoin(without crossfire) but cant for gaming.

mooo for rent
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July 16, 2011, 07:26:25 PM
 #6

My system supports Crossfire (says so right on the mobo itself), yet the secondary x16 slot operates at x4 speed when in crossfire.

Games that support Crossfire run very well, even with the x4 bottleneck.  However, some games run worse, such as Need for Speed World (the free to play NFS game), since it does not even support Crossfire.

So I just disabled Crossfire and removed the connector.

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July 16, 2011, 08:59:29 PM
 #7

In my experience I got better hashing running the cards separately than in cross fire.

Also yes you don't need dummy plugs at all if you use scripts like poclbm where all you have to do is plug the monitor cable into a card start poclbm script and then unplug the monitor cable move to the next video card start the script again, rinse and repeat.

This whole plug in and plug out is for windows of course, you could just run linuxcoin and not need to do this or the dummy plugs.
makko
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July 17, 2011, 12:20:39 PM
 #8

Cool, looks like i'm in luck then.

I can use my current media server as a miner too Cheesy:D

Well, it's an Intel DP55KG Board with Intel i5 660 3.2Ghz. (I've just put my GTX 260 in there but plan to replace with ATI).

The Mobo has:

1 x PCI Ex 2.0 x 16
1 x PCI Ex 2.0 x 8 (Bifurcated from x16 slot) (Huh?)
1 x PCI Ex 2.0 x 4

Silly question but can use any slots other than the x16 slot with ATI GPUs? Or do I need a Mobo with more x16 slots?

Thanks Cheesy

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July 17, 2011, 01:21:16 PM
 #9

Cool, looks like i'm in luck then.

I can use my current media server as a miner too Cheesy:D

Well, it's an Intel DP55KG Board with Intel i5 660 3.2Ghz. (I've just put my GTX 260 in there but plan to replace with ATI).

The Mobo has:

1 x PCI Ex 2.0 x 16
1 x PCI Ex 2.0 x 8 (Bifurcated from x16 slot) (Huh?)
1 x PCI Ex 2.0 x 4

Silly question but can use any slots other than the x16 slot with ATI GPUs? Or do I need a Mobo with more x16 slots?

Thanks Cheesy

You can use any PCI-Express (PCI-E x1, PCI-E x4, and PCI-E x8) using a PCI-E Extenders to convert to PCI-E x16

Cablesaurus sells some great cables, I have had 100% satisfaction from them. But there are other merchants selling the PCI-E Extenders and I am sure they are great as well.
macharborguy
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July 17, 2011, 01:29:23 PM
 #10

which Cablesaurus extender would be the right one to get.  I see a x1->x16 that includes a molex, and one that does not.   Not sure which would be the right one for hooking up a x16 video card to a x1 slot.

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July 17, 2011, 01:45:55 PM
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which Cablesaurus extender would be the right one to get.  I see a x1->x16 that includes a molex, and one that does not.   Not sure which would be the right one for hooking up a x16 video card to a x1 slot.

The molex one is only for when you already have 4 Video cards in a system, and you want to add a 5th or 6th.

The purpose of the molex is so that it does not draw power from the motherboard but instead the PSU.
makko
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July 17, 2011, 01:48:08 PM
 #12

Quote
You can use any PCI-Express (PCI-E x1, PCI-E x4, and PCI-E x8) using a PCI-E Extenders to convert to PCI-E x16

Cablesaurus sells some great cables, I have had 100% satisfaction from them. But there are other merchants selling the PCI-E Extenders and I am sure they are great as well.

WINNING! Does it matter about the bandwidth levels? i.e. x4, x6 or x1? Or is that just a concern when gaming and not hashing?

I have a 750W corsair in there at the minute. I think i'm gonna stick in a 6990 and see how that goes, could possible stick in a 5970 too at a later stage.

Would that PSU be able for those cards?

Also, the server is in a 4U rackmount case with 1 front fan(input) and two rear exhausts fans. I'm not sure if this would be adequate for the two above GPU's.. maybe i'd be better sliding the top off and pointing a desk fan at the cards.. opinions..?

Too lazy for a fancy sig.. Tongue
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July 17, 2011, 02:17:50 PM
 #13

Bandwidth does not matter for mining but for gaming there is performance hits, a PCI-E x8 or PCI-E x4 should be okay but a PCI-E x1 will probably be very poor performance.

Each PSU can handle multiple cards but depends on the amount of GPU's inside so for example in the 5XXX series a 5970 has 2 GPU's but the rest of the 5 series has 1 GPU, just like the 6XXX series the 6990 has 2 GPU's but the rest have 1 GPU.

750watt you could run 2 - 3 GPU's

900 can do 3 - 4 GPU's

These are my personal experiences, your experience may differ

In terms of cooling, I would suggest watching those temperatures and gauging from there, if the temperatures get to above 80C + I would find other cooling. Your going to have to experiment and see if you do need additional cooling and what would be sufficient. Personally I have floor fans cooling my PC with the cards.
makko
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July 17, 2011, 02:54:12 PM
 #14

Cool, i've just been looking into cards now and it seems that the 5850's seem like the best bet for me right now.

I'm currently trying to get two cards used at 100 Euro each.. I got this cash back in tax so if I can get them into my server I shouldn't be doing too badly.

I'll monitor the BTC/USD price over the next month and see how the cards perform. If all goes well I'll possibly get a 1.2 kw PSU for the server and stick in 2 6990's

Then put the two 5850's in my regular desktop?

Does that sound like a good plan?

Thanks.

Too lazy for a fancy sig.. Tongue
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July 17, 2011, 03:29:46 PM
 #15

Just make sure you are accepting the costs and risks of building up the rig, all money invested should be considered expendable income. Like anything else bitcoin mining is gambling and the coin price could surge or drop.

But the setup sounds like a good plan I have several rigs and one rig I have 2 5970's and 2 5850's running on a 1200w power supply.

Each 6990 should do what my 5970 do so with stock you should pull in at least 600 Mhashs per 6990
Each 5850 should do stock 300 Mhashs per 5850

So that's not bad 1800 Mhashs stock.  So about 1 BTC a day. I used deepbit's Hash calc to determine how many BTC you would get since it accounts for difficulty. https://deepbit.net/stats

Also try to minimize the amount of PC's used because of the heating affect of having 2 machines is obviously harder to cool than just one machine.
barryT
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July 17, 2011, 09:21:37 PM
 #16

Crossfire is advisible
macharborguy
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July 17, 2011, 09:33:12 PM
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Just make sure you are accepting the costs and risks of building up the rig, all money invested should be considered expendable income. Like anything else bitcoin mining is gambling and the coin price could surge or drop.

Agreed.  At the end of the day if I decide to get out of the whole BitCoin thing I will have two great cards for doing CrossFire gaming, and if all goes well this winter, by next summer it will also be water cooled.

Basically, Mining is an excuse for me to do upgrades to my PC.  hehehe

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leeloulee
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July 18, 2011, 02:02:36 AM
 #18

I dont use crosfire on my rig,,,3 6950's,,just made a couple dummy plugs and it runs great

SGT longdong
makko
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July 19, 2011, 01:01:22 PM
 #19

Thanks guys, I just secured a 5850 (New) for Euro169.. it's an ok price I think.

I'm still on the lookout for a few bargains on eBay but first I need to get some PCI Ex adapter cables..

Too lazy for a fancy sig.. Tongue
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