Originally Posted by Fieldsweeper
would it be possible
to put 4 gtx 690's (each in their own 2 way sli) or 2 sets of 4 way sli and use each of those CARDS separatly on fah core, or use a 4 way sli, and another 4 way sli on another clien in the same computer, I can;t help but think it should work.
the benefits would be great if you could run in x16 x16 8 8 or full x16 with ROX Xpander or the asrock extreme11, or maybe the RIVE and just go x16,x8,x8,x8, imagine what you could get PPD with 4 single gt690s each as a separate unit (no sli other than the internal sli with the dual gpu aspect) or as 2 - 4way sli set ups. NOT 8way sli, i know thats not possible, but something along this lines has to be doable, how else are they using tonnes of them in super computers and render farms.
the data over the SLI connector is to control AFR (Alternate Frame Rendering). Fpr compute oriented jobs, SLI is not needed, but you end up in other dependencies.
Depending on the communication pattern of the application, there might be other scaling barriers like mem bandwidth of the host. If the application is embarassingly parallel, there is not much interaction between the different GPUs individually churning happily along.
WRT to your PCI, my current experince with FAH (only doing it a few days now) is that it is quite insensitive to PCI speed.
To cut a long story short, in CFG codes (Computational fluid dynamics) your system with 4x 690s might be a bit out of balance, but for FAH which isn't using double precision FP (a design limitation in the 680 and 690 made by NVidia), you might get very good results.
You need 75 Watt delivered per socket by the motherboard. If you have a second PSU in mind you need to get the second PSU started in sync with the first one. There are solutions out there, it just doesn't work out of the box.
If my experienxe with the Titans is an indication for such a setup, for the time being a 1500 Watt PSU might suffice. The current code is driving the Kepler GPU at approx 70-75% of its TDP.
375 watt TDP per card * 75% * 4 = 1125 watt. If you take the CPU only for feeding the GPUs, the energy budget with a 1500 watt PSU is ok.
Caveat: When over time the OpenCL drivers get better and FAH improves their computational density you will have to change to a 2 PSU setup.