Does anyone have any experience with Dual Crossfire Asus ROG Matrix HD 5870?
I currently have one of these cards installed that's working very well in my setup that runs in th 65C-75C heat range under load but I plan to add a second to add some heavy-duty crossfire support.
My larger concern is configuring a Crossfire setup with these massive cards on an Asus P6x58D Premium MoBo. I have the room and space in my case and the MoBo is spec'ed to accommodate dual crossfire with 3 PCIex16 slots available.
However, the bandwidth layout is limited to x16/x16/x1 and x16/x8/x8 so if I want to really use the crossfire to it's potential I have to install these big boys stacked right on top of one another and I'm worried about airflow to the "top" card. Does anyone know if heat/airflow is a problem with this type of setup?
In theory these double-bay cards are engineered for crossfire use and most MoBo PCIe slots can only accommodate stacked configurations with such double-bay sized cards like this so one would assume there is nothing wrong with stacking these cards on top of each other so closely. But I don't like to assume and that's why there are experts on forums such as this to limit guess work/risk/throwing away thousands of dollars in damaged hardware.
What you're referring to is the total lane bandwidth available. When a motherboard senses 2 PCI-E 16x video cards installed, it'll switch that last slot to 1x mode, whichever slot that may be.
When you have 3 video cards installed, it will form into a 16x/8x/8x configuration, meaning that your Mobo only has 32 PCI-E lanes available for Crossfire (this is not uncommon).
Install the cards on top of each other as you would think to do it. The slot configuration itself doesn't matter (ex: Because most high end cards are now dual slot, one for the mobo, one for the cooler, a crossfire/sli setup will sometimes use slots 1 and 3 on a motherboard, so the motherboard will automatically assign bandwidth appropriately)
Thanks for your quick and informative response Boris.
However, upon further inspection going through the manual it looks as though my first assumption about my bandwidth limitations was correct in that the 3rd slot will not do x16 so I'm stuck with slot 1 and 2 for x16/x16 performance (as opposed to slot 1 and slot 3 to leave room in the middle for airflow). Odd because it still refers to 3 x PCIe x16 slots (they should say 2 x16 and 1 x8 because that would be more accurate)
So I guess my question is still unanswered in terms of stacking the cards right on top of each other and wondering if there are any heat and airflow issues as this does indeed look like my only option (too quick on the best answer button although Boris' answer is probably true for most other MoBos)