Another Newby Mining Rig Question

[sharky48]

Hi,

I started mining LTC the other day. But I have some questions about my rig.

I noticed that my 2 GPU's differ in Hashrate when I use the option -g 2. When I change it to -g 1, the hashrates are in sync, but not as high as with the -g 2 option.

My Hardware:
AMD Sempron 145, 4Gb RAM, 1000W PSU.
2x Club 3D Radeon R9 280X royalQueen (why is there so little info about mining with this GPU?)

My Software:
AMD Catalyst 13-12 GPU Driver
Cgminer 3.7.2, cyntax: cgminer.exe --scryptt -g 2 -w 256 -I 13 --thread-concurrency 8192 -o stratum+tcp://URL:3333 -u user -p pass  --gpu-powertune 20 --gpu-engine 1050 --gpu-memclock 1500 --temp-target 75 --auto-fan --temp-overheat 85

Temp: 75C, Fans: 3000 RPM, Hashrate: 650-700.

So my questions:
- why don't the hashrates sync at -g 2?
- Do I need to set my --shaders?
- What settings (gpu-engine and gpu-memclock) are best for my GPU's?
- With MSI Afterburner I saw that they use 1144 mV by default, can I undervolt and how much?

[jmixup]

Hiya,

Currently running 9x R9 280x's and 1x 7970.

I find that I have to tweak each individual card to get the best and most stable performance. I also found just running all the cards at the same engine clock speed's were causing the same inconsistencies.

Once your in cgminer go into the gpu settings (g), change settings (c) and adjust the engine speed (e) in small amounts and you'll find you'll get them running about the same. Temperature also plays a massive part, if ones running hotter, then it will mine slightly slower.

I don't believe you need to set your shaders if you have your thread concurrency set, but it's 2048 and won't hurt to put it in there.

[sharky48]

Thnx Hiya,

What brands (make and model) are your R9 280X cards?
What engine clock speeds do you have on them currently? So I can see how much it varies between cards.
And do you undervolt them?

[jmixup]

4x VTX 280x's < cheapy ones run between 1040 - 1055
5x Asus OC'd (default engine speed is 1100) < 1045 - 1075
1x Gigabyte 7970 < 1080

I've not undervolted any of them. I'll grab you more exact numbers a little later, that's just off the top of my head.

I'll post up my cgminer.conf too

[jvjv1]

You should be able to undervolt, I am running two Asus 280x at 1087mv on MSI Afterburner.

[sharky48]

Was your default also 1144 mv?
From what to what power usage did you go? I'm now on 620 Watt.

[sharky48]

I raised the temp-target from 75 to 80.
My 2 cards are now around 78C and the Hashrate increased to 715 and 685

I Also learned that The Club 3D Radeon R9 280X royalQueen cards are voltage locked, too bad.
My system now uses 650 Watt

[TookDk]

I raised the temp-target from 75 to 80.
My 2 cards are now around 78C and the Hashrate increased to 715 and 685

I Also learned that The Club 3D Radeon R9 280X royalQueen cards are voltage locked, too bad.
My system now uses 650 Watt

Does the Club 3D cards come with a bios switch? If yes, then is it both safe and relatively easy to flash a new bios where you have changed the voltage to the level you want. Did it my self with MSI version last week.  

My MSI R9 280X card are hashing rock stable with 1137 mV and hashing constant at 714 kH/s. The undervolting reduced them from 300W to 270W.

[sharky48]

There is a little switch next to the connector on top of the card.
Where can I find a bios to flash which is unlocked?
Can I flash a MSI bios to my Club 3D card?

[TookDk]

There is a little switch next to the connector on top of the card.
Where can I find a bios to flash which is unlocked?
Can I flash a MSI bios to my Club 3D card?

1. Take a backup of your bios by using ATIFlash
2. Modify the bios with VBE7
3. Flip the bios switch, if you mess up then can you always come back to the default bios by flipping the switch back.
4. Flash the modified bios.

Here is a good guide (I have used it my self):
http://rumorscity.com/2013/12/09/how-to-modify-video-bios-to-undervolt-gpu-in-linux/#comment-1187826533

I don't know enough about the topic to say if you can use MSI bios on other cards, but change the original bios with VBE7 and using the bios switch seams relative safe.