My experience of 3 x 7990's

[orac69]

Hi guys, noob to the forum posting my first post to enable PM's..

Ive got 3 rigs running 3 x MSI 7990's each.  All running cgminer v3.3.1 / cgwatcher mining ALT's.

The sweetspot for power / heat / not overdriving the cards Ive found to be:

0.800v
850 gpu
1450 memclock
I=19
Threads = 16384
Temps: 70-85 degrees.  (One core always runs hotter for some reason)

Pulling 620 average per core - so 1240 per card.

MSI mobo.  Windows 7.  4GB physical RAM, 8GB page file.

Power draw is around 1700 at the wall.

Im an IT guy and tried all different combinations of drivers, sdk's, tweaks, overclocks and underclocks. 

I dont know everything, but this config is solid for me.

[gamer4156]

Thank you for posting this, I have been looking at getting into mining. Are you able to run the 7990s on one psu per machine?

[medialab101]

First, I'm wondering what your PSU situation is. Second, here is the config I use with one card and I pull about 660 Kh/s:

setx GPU_MAX_ALLOC_PERCENT 100
cgminer --scrypt -o stratum+tcp://xxxxxxx:xxxx -u xxxxxx -p xxxxxx --gpu-engine 1008,1008 --gpu-memclock 1675,1675 --shaders 2048,2048 --failover-only --thread-concurrency 24000,24000 -I 20,20 -w 256,256

Finally, I want to pick up a few more of those cards. Where did you get yours and how much where they?

Thanks

[sphornby]

Not bad, I have recently got hold of some 280X's. I have 2 setup at the moment because Im waiting on some riser cables but I can pull 730 on each card, and its measuring only 600w at the wall. This is on a Richland FM2 A4000 CPU and ASrock FM2A85X. Loving this combination and cannot wait to see how much power 5 of these cards uses.

Wondering if it'll break 1500W.

[orac69]

Hi,

Sorry - I forgot all about giving the PSU info - THE most important bit !

In short, no, Ive found you cant run 3 cards on a 1250w PSU - at least not on my XFX 1250w gold - its runs for a bit, then just powers off...    I dont even think you could run them on a crazy money 1600w+ PSU as im pulling 1700w...

So I have a 1000W gold, which is hooked up to the mobo and 2 of the 7990 cards, and the 3rd 7990 card is hooked up to a spare 600w psu I had lying around.   I "jumped" pin 16 of the connector to pin 17 (ground) to get the second PSU to turn on.

Im going to add a 4th card when I get a chance for fun...

Lowering the card voltage / clocks didnt lower the draw at the wall hardly at all.

I got the cards from an online retailer in the UK who managed to get a big stock - all sold out in a day or 2 though...

I did find that putting the thread concurrency up over 16000 made the box run out of ram and crash windows - and I dont get any performance gain over 16000.

[sphornby]

Have you tried linux? There are guides online showing you how to set it up. It's pretty easy after a few initial headaches!

Key thing is to read the comments as theyre usually more up to date than the actual guides. Good bits of updated information.

I am using xubuntu and it runs perfectly.

[orac69]

btw - medialab101 - yes, I can get the cards to run 660+ BUT they arent stable - at least its not when running 3 cards.
The temps go too high, and Windows crashes / needs a restart - which loses coin if it happens overnight... I prefer to run slower, cooler, more stable.

sphornby - I have tried BAMT - which didnt run - just crashes on boot.  Im not a Linux guy, but I would like to give it a go at some point.  Thanks for the xubuntu tip - never heard of it actually...

[sphornby]

Check out this website. Good concise guide. Though I would use Xubuntu 13.04 rather than his recommended 12.10. It plays nicer with the later versions (3.7.2) of cgminer.

http://www.cryptobadger.com/2013/04/build-a-litecoin-mining-rig-linux/

[orac69]

Thanks - I will give that a try.  I read that guide about a year ago, didnt realise it had been updated with newer Linux info.  good stuff