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Author Topic: Working with and buidling around 6870's  (Read 2384 times)
Goldenmaw
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May 23, 2011, 07:45:29 PM
 #1

Well, now the 5850's are impossible to get, I've moved on to 6870's, which is good bang for my buck, as I've found a local sale on MSI Hawks for 180 each. With the difficulty growth the way we all know it is, I'm trying to brainstorm a rig to fit 4 of these as cheaply as possible. 

The specific card I have in mind:

MSI R6870 1GB DDR5
300 mhash/s (oc needed - aim for 1000 mhz)
170 approx. W each when oc'ed

I have four questions about this.

#1. Would a rig like this need special motherboard consideration beyond possessing 4 PCIex16 slots?  Would a MSI 890FXA-GD70 AMD 890FX AM3 Motherboard do the job? 

#2. I can't imagine processor bottlenecking issues would be likely, so would an AMD Sempron 140 be up to the task?

#3. Power supply - what margin of safety would you recommend given my estimates?  Would a 1000w supply be adequate? I'm definitely open to suggestions, because next to video cards we all know that choosing the right power supply factors heavily into profitability in the long term.

#4. Cooling - is this thing likely to endure the heat those four cards generate with a caseless setup? Their cores are going to need to be overclocked up from 930 to 1000 mhz, no question.  Ideal specs indicate they do best at 1000 core, but I have serious doubts as to the hardware life considering their proximity to eachother, even given the reliability of the model I intend to use.

Comments and GTFO new miner rants welcome!  I can still be talked out of this.  I haven't bought anything yet.
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compro01
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May 23, 2011, 09:34:04 PM
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1. for mining, shouldn't require anything special.

2. processor should be fine.

3. 1000W is about right.  about 850W of draw total and 1000W will give you a comfortable bit of headroom.

4. some non-standard cooling would be advised.  a large ventilation fan or something.  typical computer fans probably wouldn't do it.
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May 24, 2011, 12:29:21 AM
 #3

Would a fan like that even help?  I can't imagine that 4 cards tucked in so close together would not spell certain disaster, although I assume that there are people using a similar setup.  I'd be interested in knowing temps for cards in a similar setup.
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May 24, 2011, 01:11:03 AM
 #4

You can really only get 300 MH/s out of a 6870?

I'm getting 358 MH/s out of a 5850 clocked at 900/302.  The key is to use latest catalyst drivers/stream sdk (2.4) with the latest PhatK kernel, and downclock the ram to 300 then move up a few till you find the sweetspot

All rates with Phoenix 1.50 / PhatK
------------------------------------------------------------------------------------------------------------------------------
5850 - 400 MH/s  |  5850 - 355 MH/s | 5830 - 310 MH/s  |  GTX570 - 115 MH/s | 5770 - 210 MH/s | 5770 - 200 MH/s
minerX
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May 24, 2011, 08:59:51 AM
 #5

You can really only get 300 MH/s out of a 6870?

I'm getting 358 MH/s out of a 5850 clocked at 900/302.  The key is to use latest catalyst drivers/stream sdk (2.4) with the latest PhatK kernel, and downclock the ram to 300 then move up a few till you find the sweetspot

Try 275-300 depending on the OC.  I went with one of the low end XFX so mine can barely OC.  Stupid pricks sort through the GPUs and price the ones that OC as a higher model.
Goldenmaw
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May 26, 2011, 09:12:28 PM
 #6

The 4 card 1 board setup is as economical as you can get with a standard desktop arrangement, assuming a creative solution is found to deal with the cooling issues.  Even after considering how inefficient the 6xxx's are compared to prior models for hashing (for now), you're looking at around a 1 to 1 mhash per dollar ratio, which is great!

My design went as follows:  Diamond HD5870 1GB PCI-Express Video Card
300 mhash/s (oc needed - aim for 1000 mhz)
170 w
766 for x4

MSI 890FXA-GD70 AMD 890FX AM3 Motherboard
191.60

WESTERN DIGITAL 160GB CAVIAR BLUE
26.61

DDR3 2GB PC1333 SO-D CORSAIR
26.61

AMD Sempron™ 140
39.39

Antec TruePower Quattro TPQ-1000 1000W ATX
191.68

For a total of 1241.89 spent to gain 1200 mh/s.  Not bad.  The philosophy is obvious - get as many of the most efficient cards hashing and minimize expenditures on everything else. The same design with 58xx's would push the cost efficiency even higher.  However, given the difficulty doubling we'll be seeing for some time, I can't justify getting into mining just now.  I don't see the difficulty spikes slowing down for many months, as growth will continue even after people get burned on setting up new rigs, thanks to people allocating rigs they already have to mining.
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May 26, 2011, 11:49:29 PM
 #7

I'm late to the party guys...

Anyhow, I got my first upgrade card in today.  I got an xfx 6870 which is currently running @ 265Mhash. 

I'm using guiminer and when it first starts mining, it's at around 325 but then drops down.  I had the overdrive settings cranked up, but my system hung twice ( temps were only 60c ) so i'm not really sure why it hung but i dont want to leave it and think it's mining only to find out that it's hung up...

Anybody have problems w\ their 6870s like that? I'm using flags -v -w128 -f 1

overdrive : 67c , 96% activity, 45% fan speed

The fan @ 70% sounds like a server on boot up lol.
kjj
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May 27, 2011, 12:06:42 AM
 #8

I'm late to the party guys...

Anyhow, I got my first upgrade card in today.  I got an xfx 6870 which is currently running @ 265Mhash. 

I'm using guiminer and when it first starts mining, it's at around 325 but then drops down.  I had the overdrive settings cranked up, but my system hung twice ( temps were only 60c ) so i'm not really sure why it hung but i dont want to leave it and think it's mining only to find out that it's hung up...

Anybody have problems w\ their 6870s like that? I'm using flags -v -w128 -f 1

overdrive : 67c , 96% activity, 45% fan speed

The fan @ 70% sounds like a server on boot up lol.

I picked up a pair of them a while back.  One is doing 263.75 Mhash/sec at the stock clock speed.  If I overclock it, it crashes.  The other though, can run all day overclocked to the stock BIOS limit of 1000 MHz, and it turns in right around 300 Mhash/sec.

6870 is an excellent card, if you get a good deal on it.  When I was doing my shopping spreadsheet, it was worth 1.71 Mhash/sec per dollar.  The next closest was the 5850 at 1.52 Mhash/sec per dollar.

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airdata
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May 27, 2011, 03:55:51 AM
 #9

I got it for $187.99 on amazon and it came w\ a game that I sold for $15, and it also has a $20 MIR so after MIR should be around $150 for it. 

After those initial system hangs, i bumped the speed down and it's cruising along @ 268 Mh.  Temps are awesome compared to my 4870 it replaced.  It's under 99% load w\ fan @ 45 and it's only in the 60's.

W\ the recent difficulty increase I'm a little bummed I didn't get in sooner.  Will have an additional 5770 up and running tomorrow and then another 5770 a couple days after that.
bcpokey
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May 27, 2011, 04:39:19 AM
 #10

6870s yield terrible MHash/$. Well I shouldn't say terrible, but it is quite poor, if you buy new it's one of the few reasonable options left I suppose. Buying used is a far superior option if you can wrangle it though.

@OP the MSI 890FXA is a good board, can do 4 cards definitely though a bit pricey. If you can find a cheap board and buy some PCI extenders you can save yourself a few bucks. You don't need x16 slots, x1 slots work fine. One warning, hawks are custom coolers, they might not fit into standard 2 slot spacing.

Processor contributes essentially nothing, sempron 140s are ideal.

1000Watts is ridiculous overkill for 4x 6870s. You are essentially throwing money away unless you found a good deal on a 1000Watt PSU. One of the 6870s best features with the reduced processor count is improved power efficiency. If you downclock the memory a 750 should be plenty. Getting a high quality matching wattage PSU is far superior to getting a higher wattage junk PSU. tx750s can be found for $100 easily.

Cooling... The 4 cards are going to JAMMED together. Depending on the cooler the card is equipped with it will handle this with varying degrees of compliance. Risers or extenders are a good idea. If not, you will need to press them apart in some way and force air in between them with a fan setup of some kind. Otherwise you will have problems with sandwiched cards, crazy loud fans, overheating and so on.

I'm not sure I'd do this buy however until you calculate if the return will be worth it. Just a fair warning.
lastobelus
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May 27, 2011, 05:14:03 AM
 #11

4 X 6870s stay cool enough if you have a side fan. I'm using a coolermaster haf x, it has a large side fan. Can't run all four cards overclocked without the side panel on, but with it on I stay below 70C.

They are noisy though.

Also, they won't all go to 1000

And some of them need to be kept really cool to be overclocked, like under 70.

Don't forget you will need adapters, molex to pcie and/or cpu to pcie, because the cards require two pcie lines each, and power supplies will have only 6

I deliberately bought a really good power supply because it was on sale and I intend to use it somewhere else later. But even that had only 6 pcie connectors. Maybe there are psus with 8, but I don't know any.

I bought 6870s because at the time, in Vancouver with ncix sale, they were definitely the best mhash/$. Currently 6950 is slightly better. IF you buy them separately so you get rebate on each -- buy them all at once and you only get one rebate!
kjj
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May 27, 2011, 07:49:03 AM
 #12

6870s yield terrible MHash/$. Well I shouldn't say terrible, but it is quite poor, if you buy new it's one of the few reasonable options left I suppose. Buying used is a far superior option if you can wrangle it though.

Opinions vary.  When I did the math, it gave the best Mhash/sec to $ ratio, and by a considerable margin.  Also, it was in stock almost everywhere.

Anyone that is thinking about mining needs to make a spreadhseet and list all of the options along with their hash values.  Then shop a bunch of sites, looking for the best price on each card.  From there it is a simple matter to find the best Mhash/sec per $ value.  Adding electrical costs (if such apply to you) to that spreadsheet is trivial.

p2pcoin: a USB/CD/PXE p2pool miner - 1N8ZXx2cuMzqBYSK72X4DAy1UdDbZQNPLf - todo
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