Author Topic: 6 Card Build - R9280X  (Read 3980 times)

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Offline 2LTCTopic starter

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6 Card Build - R9280X
« on: November 29, 2013, 07:56:53 PM »
What all do I need to put together a 6 Card Build compiled of R9280Xs for LTC mining?

I had this together so far:
Six (6) XFX AMD Radeon R9 280X 3GB Cards @ 319.99 each
One(1) MSI Z77A-GD65 LGA1155 Z77 Motherboard
Two(2)Coolmax ZPS-1600B 1600W 80 PLUS Silver Power Supply w/ Active PFC -- OR -- LEPA G Series G1600-MA 1600W 80 PLUS Gold Power Supply???
Six (6) Powered 16X to 1X PCIe Riser with Molex Connector ( newbielink: [nonactive])
Six (6) PCI-E Express 16X Riser Cables (Looks like 16X to 16X - newbielink: [nonactive])
One(1) Corsair Vengeance Blue 4GB RAM
One(1) Intel Celeron G1610 LGA 1155 Processor
One(1)Add2PSU device to make 2 PSUs work together

What else am I missing for this build? I assume I will put 2 cards directly into the mobo, use a 16X to 16X riser for the 3rd PCI-E slot and then use the 1X to 16X risers for the other 3 cards? Will I need to underclock the GPUs in the 1X slots so it doesn't burn up? I assume using the cards under the 1X-16X will mean they're not as efficient as the 16X-16X ones.

Offline Probopass

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Re: 6 Card Build - R9280X
« Reply #1 on: March 13, 2014, 02:48:02 PM »
I think that you can cut back on the power supply.  I read this that you have two 1600W units and you can probably get by with an 850 and a 1200.  Use the 850 to power the MB and two cards (which will put you at about 700 watts - right in the efficiency range) and then the 1200 to run the other 4. 

I think that 4GB is too little.  I am running BAMT and it is using 8 GB on just 2 cards.  Remember that the way that the program talks to the graphics cards is through the memory on the main board and part of the graphics memory on the GPU is shadowed in regular memory.  I do not know the exact amount for all 6, but I have heard a rule of thumb is 2GB per card plus the OS. 

If you only have 6 cards you only need 6 risers and you are listing 12.  It is my understanding that the fires come from the riser cables - as you reduce the voltage the amperage goes up and running more amperage through those tiny wires causes the problem.  I am using the risers with the USB cables and I am seeing zero problems and I have better airflow without the ribbons.

You can put the 1x into the 16 slot(s), but you might need to jumper the slot on the MB to make sure it knows that it is in use.  I have seen people saying both directions on this and so I expect this is MB/OS/BIOS dependent.  You are not worried about graphics performance, just the conversation to the PCI-E - so you will not see a hash rate performance gain using the 16x over the 1x. They will also not run hotter just because they are in a 1x slot.  Typically you undervolt to save power and heat and overclock to get more hashes per second.  You just have to find the sweet spot where you do not undervolt so much as to create hardware issues and you do not overclock so much that you don't overheat the GPU.  The power coming through the wires in undervoltage creating more amps.  The formula is (watts = amps x volts).  As you overclock you use more watts and by undervolting at the same time you only leave room for one of the elements to move - amps.  Putting higher amperage through a tiny wire is where fires get started.  Typically, the system will shut down before damage occurs, but you can burn up a MB, a riser or a card very easily.  Tune these in small steps.  Install just two cards first, leave the first one stock and attach your monitor to that one so you can get into the bios and start and stop the miner, then tune the second one.  When you get the second one running right, copy the parameters to the rest of the cards and go for it.

By the way, you will see different hash rates on each card.  Each GPU has a quality code and that goes into the voltage that is in the bios from the factory.  You will see different voltages on the cards.  The lower the voltage, the better the GPU.  Take that into consideration as you tune.

Hope that helps.
« Last Edit: March 13, 2014, 03:08:56 PM by Probopass »


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