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Old 07-09-2009, 10:10 PM   #1
Registered: Sep 2008
Distribution: Kubuntu 11.04
Posts: 85

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SLI with PCI Express and PCI Express 2 Cards?

Hi guys, I'm trying to set up SLI under Fedora 11 with my existing Nvidia GeForce 7900 GS and my new GeForce 9500 GT.

I've installed the drivers and my system is picking up both cards. I've also added the SLI option to my Xorg.conf file. However, looking in the Xorg.o.log file shows these errors...

(**) NVIDIA(0): Option "SLI" "on"
(**) NVIDIA(0): Enabling RENDER acceleration
(**) NVIDIA(0): NVIDIA SLI auto-select rendering option.
(II) NVIDIA(0): Support for GLX with the Damage and Composite X extensions is
(II) NVIDIA(0):     enabled.
(EE) NVIDIA(0): Failed to find a valid SLI configuration.
(EE) NVIDIA(0): Invalid SLI configuration 1 of 1:
(EE) NVIDIA(0):     1) NVIDIA GPU at PCI:1:0:0
(EE) NVIDIA(0):     2) NVIDIA GPU at PCI:3:0:0
(EE) NVIDIA(0): Errors:
(EE) NVIDIA(0):     - GPU architectures do not match
(EE) NVIDIA(0):     - GPU implementations do not match
(EE) NVIDIA(0):     - GPU PCI IDs do not match
(EE) NVIDIA(0):     - GPU video memory sizes do not match
(WW) NVIDIA(0): Failed to find a valid SLI configuration for the NVIDIA
(WW) NVIDIA(0):     graphics device PCI:1:0:0. Please see Chapter 25:
(WW) NVIDIA(0):     Configuring SLI and Multi-GPU FrameRendering in the README
(WW) NVIDIA(0):     for troubleshooting suggestions.
(EE) NVIDIA(0): Only one GPU will be used for this X screen.
Now my GeForce 7900 is a PCI Express 1 card while my GeForce 9500 is a PCI Express 2 card. So simply, is my problem the two different interfaces? If not, my board is an Evga 680i. It says it supports SLI but it does not explicity support PCI Express 2. As far as I understand PCI Express 2 is backwards compatible with PCI Express 1. If that is the case, I guess I'll be buying another 9500. Sounds like a good excuse to upgrade.

Thank you for any help. It is greatly appreciated. Also, I'm aware that apart from me using SLI under Linux, this has almost nothing to do with Linux but I don't know where else there is such a high concentration of intelligent people on the Internet that may be able to help me.
Old 07-09-2009, 11:28 PM   #2
LQ Guru
Registered: Jan 2002
Posts: 6,042

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It will be nice to see from the very start and then to the end of the log. Snipping it does not help and I do not like it. I think it is recognizes two different graphic cards of the different models which you have. nVidia's documentation on how to setup SLI is informative about the assigning of addresses for each card and about the requirements of SLI. From what I read and common sense, SLI will only work if two or more cards are equal models. A GeForce7 7900 and a GeForce9 9500 are not equal, so SLI will not work.

Since you are going to buy a video card, spend the money on a GeForce GTX 285. It provides more grunt than two GeForce9 9500 in SLI mode and with more compatibility with any program. You can then use the GeForce9 9500 for a secondary video card. You can watch a HD video on the GeForce9 9500 with the help of VDPAU and play a game on the GeForce GTX 285
Old 07-10-2009, 08:41 PM   #3
Registered: Sep 2008
Distribution: Kubuntu 11.04
Posts: 85

Original Poster
Rep: Reputation: 15
I looked into getting a GTX 280 but, unfortunately, the only thing stopping me from getting it is that it simply won't fit in my case. Besides, I only want two cards for CUDA and the possibility of going to a tri-monitor setup in the future. The 9500 should suffice for that. Anyway, I ordered another 9500. I'll try it all again when it arrives. Thank you for your help Electro.


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