Bitcoin Forum

Guys, any thoughts dual 6990s?

Can I use any miner for the job? Do you expect hash rates to increase as drivers get better?

Would you opt for 4 X 5870 instead?

I'd like to hear from people already using them as well.

Many thanks

Dual 6990s would do a fine job

Thanks for that. Would you as a miner get them over 4 5870s?

I'm about to get a rig... But can't decide. It's fair to say that both have their advantages.

yes because when mining isn't very profitable, or if BTC crashes, you got a great GPU system, while 4x 5870 won't be worth anything. Besides, 2* 6990 is supposed to have a higher Hashrate than 4* 5870. Also, considering power draw, heat, space and motherboard needs, the 6990s are much better

Are you certain? I'm almost positive two 5870s will beat a single 6990 by a good margin at pure hashing power. Have you seen a 6990 hit over 700Mhash/s?

Also, isn't the 5970 faster than a 6990 while using less power?

I think the only drawback of the four 5870s is the spacing (and thus cooling issues) on a single motherboard. It will take more power to run 4 of them vs. 2 of the dual core cards, but you will be getting more hash/s from a single machine (which may or may not be cost effective).

My thoughts

5990 - I really think the the 5990 is underrated because not many people have been under the hood yet to fine tweak the miners, Hence the mundane stock rate right now of 0.6Ghps. But I read somewhere  that the card could potentially be 28% faster (not sure if some of that can be used for generating coins)

Also, the card will have a lot of resale value, miners will take most and what's left will be for the verrrry wealthy gamers and since this card is produced in limited quantities prices will go up.

2 * 5990 1.2Ghps 800ish Watts. 

CONS

The card consumes a beastly amount of energy - some quoting 445w under load.

5870 - two of these cards will give you 0.7Ghps, require less power, it can even be economic to just have in 4 in 2 crossfire motherboards (tri + quad fire way to expensive) Needing cheaper PSUs

4 * 5870 1.4Ghps 750ish Watts.

Man... My balance is 0.05 thank you faucet!

I think you mean 6990 when you say 5990? Have you looked at the 5970 compared to the 6990?

With some searching, there are used, last generation, quad pci-e x16 boards to be had for much less than you'd expect.

The 6990's Power consumption after mem clock reduction, is lower than that of a 5970 after reduction

2* 5870 takes 424W, 1* 5970 = 304W, 1* 6990 = 338W. This is without downclocking mem. The 6990, with it's massive 4GB and higher mem clock, has more benefits from the downclock, hence, less power usage than that of a 5970.

A 6990 outperforms a 5970, so I'm guessing it outperforms 2* 5870s too. If not, then it isn't far. Best $/Mh is still the 5970. I'd still get 6990s as I find investing in old tech for something that isn't for sure is not smart, at least the 6990 has resell value and better usability in other applications

Interesting, I hadn't heard this about the 6990 elsewhere.

It would be fantastic if there was a simple way to decrease the voltage to the memory on any of these cards. I have yet to find a solution on the web.

care linking your source? I've got different numbers:

http://benchmarkreviews.com/index.php?option=com_content&task=view&id=706&Itemid=72&limit=1&limitstart=16

5970 on load = 299W
6990 on load = 350W

This indeed doesn't take in account the power saved through ram underclocking, and i think it is quite possible to get the 6990 to run in the lower 3xx, but I doubt it'll fetch below 300. I don't know how faster the 6990 is compared to the 5970, but I wonder if it justifies the $700 price tag considering you can get 5970s on ebay for less than $450 shipped. At any rate, you can get three 5970 for the price of two 6990. Better $/MHash for sure.

As for four 5870, they'll definitely draw more power than two 6990. Although single gpu cards o/c much better, so I wonder if a 6990 combo could beat four 5870.

One 6990 beats two 5870 because the VLIW4 architecture is easier to fully exploit than VLIW5 arch. I benchmarked my miner, hdminer (http://bitcointalk.org/index.php?topic=2949):

• One 6990 (switch at position 2, ie. 830MHz): 683 Mhash/s
• One 6990 (switch at position 1, ie. 880MHz): 723 Mhash/s was an error, I measured: 746 Mhash/s
• Two 5870: 664 Mhash/s (332 Mhash/s each)

However, price-wise it makes more sense to buy two 5870.

5870's can squeeze 360mhash each with an average o/c on stock voltage.

Apples vs. oranges. The 6990 too can easily be overclocked beyond the "factory" 880MHz.

Of course it would. Bitcoin mining scales linearly with the # of GPUs, so a pair of 6990 at 880MHz would achieve 1446 Mhash/s, compared to 1328 Mhash/s for four 5870.

It is kind of pointless to argue which one would be faster when overclocked beyond the factory setting, because the overclocking room varies so much from card to card, and with the type of cooling (air, water, etc).

Do you happen to know the power consumption of that card at 723 Mhash/s?

a question on that subject was brought up, so i answered it.

The point was that even though the 5870 is the worst Mhash/W ratio of the 3 choices mentionned, it's the best Mhash/$, partly cause it can overclock so well when compared to dual gpu cards. This is relevant to the choice of cards imo.

Now, let's admit that four 5870's hash like two 6990, it would cost $700~800 to get the 5870s off of ebay, and $1400 for the cheapest 6990's out there. At worst this is a $600 difference. Assuming the 5870's run at 200W/h and the 6990 at 250W/h (im taking large figures here on purpose) you'd be at a 300W deficit per hour with the 5870's. At an expensive $0.20/kW(exagerating figures again), you'd be paying an extra $1.44 electricity per day compared to the 6990's. At this rate, the 6990's will close the gap in 416 days, or a little short of a year and 2 months. I'd take the 5870's, not to mention that you can build up to it slowly with the profit generated by cumulative card purchase.

I agree with you goatpig. I said from the beginning that price-wise the 5870 is more economical.

Indeed. Anyways, do you have extra data to share on the 6990, like power consumption, how low can the ram be underclocked and what not?

http://tpucdn.com/reviews/ASUS/Radeon_HD_6990/images/power_maximum.gif

from http://www.techpowerup.com/reviews/ASUS/Radeon_HD_6990/20.html  Their reviews are the best on the web IMO. One of the reasons I'm an active member over there. These are max figures, meaning the most you could draw from the card (ie: 100% load Furmark etc etc). I do not know if the power consumption is for 830Mhz core, but I believe it is. In your review, they state that the power consumption goes up by 18W for 880 core, so total Power consumption for the 6990 st 880Mhz should be 356W. There is a memory voltage bump, I believe, between the 2 BIOSes however, so keeping the 830 core BIOS but OCing to 880Mhz and downclocking to 150 mem (default idle clock, which is much lower than that of a 5970!!!) should definitively drop the Power consumption. I'm inclined to say that 5970 at 5870 core speed and 300 mem would definitively need more power than a 6990 at 6970 core speed and 150 mem.

I believe 6990s are the way to go, as the VLIW4 architecture is the future for AMD and they have some potential in terms of developing their drivers.

One of the main reason the 6990 has approx 50w more power draw than the 5970 is because of the 4 GB memory, if you underclock that, you should have lower power consumption than the 5970.

There are many reviews that use the unleashed mode (hardly any benefit) and thats where you get the apparent massive power draw from.

On top of that the 6990 also features power tune, I'm using it on my 6950s (-11%) it reduces power consumption substantially and doesn't affect the hash rate.

Oh and 6990 has resale value and is a monster when gaming ;D!

True, the 6990s power consumption should be lower, but it would be awesome to know how much lower. The chart gives some figures to work with, but it would be great to have some data from actual miners as well. I have a 5870 that differs 27W from the chart, for several reasons I'm sure. It would be great to see how much the 6990 can benefit from a memory underclock. It certainly seems like there is a lot of potential there.

I'm looking for reasons to justify the 6990 in a hashing machine. For me, it all comes down to value. New tech is fun and exciting, but if there is minimal benefit for massive price increases, there is no point for me to spend the extra money.

As far as resale value, every day I see used 5870s selling for more than I paid for a new one.

The machine they use to take the power from that is a Keithley Integra 2700, a 1600$ machine that measures from the pci-e slot.... W1zzard has been into reviewing since a long time as well.... I believe his results are very accurate

I wasn't suggesting that the results on the chart were inaccurate. He doesn't underclock his memory, which is my primary concern. Also, he probably isn't mining when he takes those readings! Hmm, his method wouldn't account for power supply efficiency either.

If it did, it wouldn't be accurate would it? No reviewer should EVER take into account PSU efficiency. PSU efficiency is not constant, nor is it the same from PSu to PSU, even if it is the same model

If you have a good PSU, you can say your efficiency is about 80~85% though. to give an idea, at 356W, with 85% eff, it takes 418.8W AC.

Let me clarify. I don't necessarily care how much power the cards consume, other than it's a nice guide. I care about how much power the cards consume when mining bitcoins (to the best of their ability)!

When comparing, you CANNOT take that number unless you are talking theoretically. Else it is VERY innacurate. at 356W, at 80% it takes 445W while at 85% it takes 418W. It depends on too many factors for it to mean anything

Do not forget that if you are solely using you computer for mining, you might as well take into consideration whole system power consumption. 

I never said he should, just that he didn't. This is a good thing. It was merely a comment on some of the things that vary from his chart to actual mining usage!

Of course I take into consideration whole system power consumption. Why would I be concerned about how much power is saved from underclocking the memory if I wasn't looking to save power elsewhere? That said, most of my power consumption comes from the video cards. I am bothered about CPU usage with multiple cards in Windows though.

Again. Those numbers are a great guide, but I'm more concerned about actual mining usage. The main thing I'm looking for is how much power is saved on a 6990 by underclocking the memory, as it seems like it could be significant. His chart does me no good except give a reference point of max consumption. It would also be interesting to know if the card supports undervolting the memory.

Undervolting memory may only be supported through BIOS mods...

it would be interesting to know about power consumption at lower mem clocks. If you REALLY want to know, I can ask him, provided I give him enough $$. I would need something like 15~20$ I guess. If enough people want this and contribute, I can ask him ho much he wants, perhaps he would do the same for a 5870 and 5870 if he still has those too.

I've checked all of my current BIOS (5850 / 5870) and unfortunately I can't access the VTT registers in any of them.

I do want to know, but I'm patient and not looking to purchase any 6990s in the very near future. I'm sure there will be miners that use them and are willing to provide their info. While it may not be as accurate as W1zzard's, it will be interesting none-the-less.

Okay guys, thanks for all of the feedback. There has been some repast good discussion here. It amazing how members of the community contribute so much.

Well ive decided to go for a rig that consists if 2 x 6990s

My next rig will most probably be a trifire with 1 x 5970 and 2 x 5870 (eta 3 days)

The 6990s will arrive tomorrow.

I can unbox and give my initial results if you like.

Results would certainly be appreciated!

Which ones did you get, and have there been any overclocking comparisons among the various brands?  I imagine they are all reference designs at this point.

they are all mostly reference

Yep:

HD 6990 (@sw1, 880MHz): 746 Mhash/s, 410 W, 1.82 Mhash/J
HD 6990 (@sw2, 830MHz, default): 708 Mhash/s, 346 W, 2.05 Mhash/J
HD 5970: 569 Mhash/s, 275 W, 2.07 Mhash/J
(Measurements taken while running hdminer, with a clamp meter at the three sources of power: slot + two power connectors.)

I would not recommend to mine at 880MHz since it is about 8% less power efficient than at 830MHz. Also, contrary to what is believed, the Mhash/J rate of the HD 6990 is not so bad at 830MHz when compared to the good old 5970.

can you try with mem clocks at like 150 for the 6990 and 300 for the 5970 please? :D

Too late. They are racked and mining. Sorry :-\ I will have more time for optimizing the power consumption when/if I get a next batch of cards.

guys, how do I go about reducing the mem clock using ubuntu? As I understand it one could use afterburner under windows but I am not too sure about ubuntu.

Doesn't help on linux, apparently, althought yet to test this myself ... you might find some useful tips here.

http://bitcointalk.org/index.php?topic=4806.0

I think you might have your hands full just getting the 6990 up and running on ubuntu with full driver/OpenCL support etc ...

Awesome! Thanks for posting this.

I accidentally mined a load of bitcoins when I left the client running on my server for a month last year.
I discovered them a couple of weeks ago - so immediately decided I liked bitcoins and I should use the cash to buy a new rig - i7 with two 6990s fed with a Corsair 1200W.
Can't speak of the power consumption of the individual components, but I can get the wattage the whole box is drawing from the plug.

Whole system running at stock speed originally pulled about 920W. Once I'd sussed that I forced each of the poclbm processes to all use the same CPU core, that dropped to about 850W.
Upping the GPU speed to 850MHz and the memory down to 625Mhz (For some reason even fiddling with config file, I can't get afterburner to allow lower), it now happily runs at 720W.

I'm pretty sure I've still got some 'issues' with the system though. I'm currently using poclbm and that's giving me ~340MHash/s per GPU core. Not good, but not bad - tried poclbm-mod, phoenix and even after playing with config for a bit, still can't get any noticable speed increase. Strange thing is that if I up the GPU cores (giving a little bit more voltage), it doesn't seem to make any real difference in speed and just starts to guzzle the power.
Only thing I can guess is that there's some kind of bottleneck somewhere. Currently it looks like I need to have Crossfire enabled (without it only see 2 GPUs and they don't seem to run as fast). Going to have a play with some resisters to make a dummy plug when I have some time.

#edit - just realized I had some resistors in a drawer over my desk so have it a go - no luck. I just see Cayman core 0 and 1