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Author Topic: Hardware bottleneck on Quad System.  (Read 641 times)
Striker
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August 29, 2011, 09:25:58 PM
 #1

Hi,

This is a post about hardware but I am still a newbie so here goes:

I want to begin mining and I am about to go for a Quad 6990 system.
I have zero experience in mining rigs but this would be my start system:

MSI 990FXA Mobo
4 X 6990
2X 1000W OCZ PSU
I will get riser cards and pci-express feed power directly from PSU and the all stuff lots of air cooling the all enchilada.

The components I am not really sure for this system are the amount of memory for such a system and the CPU.
Should I get a X6 Six core AMD Phenon or a cheaper quad AMD Phenon ?

What about memory?
4GB ? 8 GB ? or just 2 GB ?

Also another issue about this is the possible bottlenecks and tradeoff's of such a system.
The PCI-e buss will be crowded.
Also this is equivalent of having 8 6-series GPU's ... the 6990 are Dual-GPU cards.
Would'n there be a bottleneck on the PCI bus because of such crowded system demand ?


Regards.
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shadeless
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August 29, 2011, 09:30:47 PM
 #2

somebody correct me if im wrong, but cpu and memory are more or less irrelevant for mining. you can use cheap stuff there.

in regards to the pcie bus - mining doesn't use much bandwith, so that shouldn be a problem, as long as the cards dont draw to much power from the bus (which you prevent by using riser cables/cards with direct psu power feed)
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August 29, 2011, 09:42:16 PM
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Hi,

My issue about the pci-e bus is not about electrical and signal integrity, that will be assured because of the direct PSU feeding.
The problem is having 8 GPU's always accessing the bus ...

I would like to have some hard numbers from some experienced user with this type of setup ...


Regards.
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August 29, 2011, 09:51:16 PM
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The problem is having 8 GPU's always accessing the bus ...

I would like to have some hard numbers from some experienced user with this type of setup ...

thats what i meant with bandwith, not much data passes through the bus while mining compared to gaming or the like. people even use pcie 1x slots to mine with their gpus. but i can't provide you with hard numbers, sorry. lets wait for a more experienced user.
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August 30, 2011, 04:51:11 AM
 #5

I don't think the bandwidth is the issue.  PCIe x1 will give you enough bandwidth.

Some people have set up quad 6990s (I have seen pictures), but I am not sure how well they run.  See: https://bitcointalk.org/index.php?topic=36182.0;topicseen

although I think 3 runs fine: https://bitcointalk.org/index.php?topic=7216.msg488820;topicseen#msg488820

the problem with the 6990s is that they are essentially impossible to buy new from any vendor at a reasonable price.
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August 30, 2011, 08:42:01 AM
 #6

Hi,

Oh! I agree about the price!

The thing is according to my calculations they are the only boards with the best price/(MH/s ) right now.

What about CPU and memory??
What is your view/experience?

Just to make clear: They will of course all run Linux.


Regards.
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August 30, 2011, 05:04:23 PM
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Yeah, the 6990s have very good Mhs/s and Mhs/watt, besides the heat and the noise.  I think that's why they are so hard to find because everybody wants them.  Both Amazon and Provantage have been out-of-stock for awhile.

CPU and memory just have to be at the minimum since mining doesn't utilize them.  People have used AMD Athlon II X2 250 for AM3 and Pentium G620 for socket 1155.  There is a bug that causes the CPU to be utilized but I think that is only with a certain Catalyst drivers.  For Linux, it sounds like people like LinuxCoin.  For memory I think a 2 Gb stick will do.
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August 30, 2011, 06:11:30 PM
 #8

Neither your cpu nor memory will bottleneck you in any way.Buy the cheapest things you can find.In fact i think your PSUs are overckill as well.I have miners with 1x6950+3x5830 with cheap CM gx650 and they are fine.
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August 30, 2011, 06:49:42 PM
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Hi,


Thanks for your answer.

Neither your cpu nor memory will bottleneck you in any way.Buy the cheapest things you can find.In fact i think your PSUs are overckill as well.I have miners with 1x6950+3x5830 with cheap CM gx650 and they are fine.

I think that for a price issue only I will go for Dual Core Athlon X2 3GHz... they are cheap enough and they are only 65W maximum TDP. So that is just fine.

About memory it will be ok too. I will go anyway with 2X2GB DDR3 1333MHz. They will cost me about 20 euros so ... not very expensive either.

About the PSU's.

Each 6990 can drain 375W not overclocked. I will not overclock any board anyway.
But not overclocked they can drain 375W.
4X 375 = 1500 W, (1.5KW  Shocked  )
Say the rest of mobo + CPU + fans = 100W  max
Total system power consumption will be = 1600W

Almost all power supplies have and efficiency curve that depends on their load. Usually the maximum efficiency is at 50% load.
My OCZ PSU's (combined 2 X 1000 W) system will operate at Maximum Efficiency of 90%. (They are rated at 92% at 50% load).
If you choose a Less Powerfull PSU you will not only be outside the maximum efficiency of your PSU's, therefore Increasing power costs for the same MH/s result, but more importantly you would be Pushing the limits of the components on those PSU's, thereby limiting there life expectancy (MTBf at higher temps) and increasing overall heat inside your box.

I think that in systems like these the PSU is paramount not only from a efficiency stand point but also for system stability and long term operation.
I can make savings on all components Except on the PSU's ...


Regards.
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August 30, 2011, 09:21:21 PM
 #10

Yes i like good power supplys too but when it came to making a mining rig i made a lot of math and i could't justify a higher price with 2% lower electricity[the difference between lets say bronze and silver PSU,and the difference between a PSU at 95% load and 60% load is even smaller ~1-2% when we talk about nice PSUs].And then also i think the commonly cited usages of the cards are exaggerated but i have not made any measures.
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