crossfire or not?

[ibrahim11]

I have 2 msi 280x twin frozr gaming edition gpu's.  Should I use crossfire? Thanks

[kalus]

no.

[Fastpow]

no.

And why not?

[JL0z]

Cgminer and other miners will utilize all gpu's installed in the system - those that are configured, that is.  There is no need to use crossfire to combine them - actually this might make it hash less.  I did have 3x 7950's on one machine running Linux, all hashing well - until one 7950 decided to have a fan failure, now waiting on a replacement.

If you were gaming under Windows, and wanted more performance, then yes - crossfire them.  You can still use the machine for mining when not gaming.

[breakbeater]

I have 2 x 280x from MSI in Crossfire and they hash more stable @ 735 kh in CF mode and GPU0 @ 680kh / GPU1 @ 735kh when CF is disabled.
I use cgminer 3.1.1

[Kenshin]

Cgminer and other miners will utilize all gpu's installed in the system - those that are configured, that is.  There is no need to use crossfire to combine them - actually this might make it hash less.  I did have 3x 7950's on one machine running Linux, all hashing well - until one 7950 decided to have a fan failure, now waiting on a replacement.

If you were gaming under Windows, and wanted more performance, then yes - crossfire them.  You can still use the machine for mining when not gaming.

+1 I have tried mining with Cross FIre, and the hashrate are much slower.

[breakbeater]

I guess i am the lucky one, mining in CF @ 735kh with default settings.

[JL0z]

I guess i am the lucky one, mining in CF @ 735kh with default settings.

Definitely!  Even though people use the same configuration, each card actually is different.  For example, when I was running 3x 7950's at default clocks, each 7950 would give me 582Kh individually, but together - only the first gpu gave me 582Kh, the other two only got 530Kh or so - when running at intensity 18.  However, if I bump up the other two cards to intensity 19 each, then all three would give 582Kh.  With overclocking, they can get 630Kh without getting two hot, but here in Australia - it is summer, so I don't like the gpu's getting to 90 degrees, so am keeping them under 85 degrees - once we get to winter, I can run them harder.

[Edit]  Also, the cgminer version does make a difference - the latest is not always the greatest.  I am running 3.7.2 - the last version to support gpu's.  I feel that 3.6.6 was giving me slightly better hashing, but am staying with 3.7.2.

[RB25]

They way it was explained to me was that when you Crossfire or SLI, the cards have to communicate with each other as well as perform the designates task. This causes some card resources to be allocated to communication rather than hashing.

Or did someone tell me wrong?

[JL0z]

They way it was explained to me was that when you Crossfire or SLI, the cards have to communicate with each other as well as perform the designates task. This causes some card resources to be allocated to communication rather than hashing.

Or did someone tell me wrong?

That is correct.  When you see the games performance gain with crossfire or sli, it isn't +100%, but generally +90-95%.  However, each card is different, and it must be possible that in some cases, crossfire actually performs better than individually.  I know that my cards don't do the same as reported by others - I have to set different intensities to get the same hashing rate across the cards, so either something in my configuration is doing this.  By the way, some people say that we must use dummy plugs, and others say it isn't necessary - I only have a monitor connected to the first card, and nothing on the others - maybe I should try the dummy plugs, anyway, just a thought.

[kalus]

no.

And why not?

because mining.

[FilipZ]

I guess i am the lucky one, mining in CF @ 735kh with default settings.

maybe 735 is less than 735+695
or is it 2x735? so it should be 1470?
how many GPU's are in miner 0,1 or 0?

[breakbeater]

In CF i have 2x735kh and with CF disabled GPU0 (680-690kh) + GPU1 (730-735kh)