P6T + 3 way SLI + 12GB ram = stupid slow?

C

CrazyRob

[H]ard|Gawd
Joined
Aug 26, 2004
Messages
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I've run into an issue I haven't been able to find with any amount of googling. Building up a rig based on the plain Asus P6T. I've got 3 identical EVGA GTX 285's and two identical matching kits of 3x2GB Corsair Dominator DDR3 1600. All assembled, it takes about 45 minutes to get to the desktop (posting seems to be about normal speed) as well as memtest takes about 3 hours to test all the memory (but it does pass without error).

If I reduce it to 3 sticks of ram, everything works fine, but if I add a 4th, 5th, or 6th stick of ram, this problem comes up.

Additionally, the system works fine with all 6 sticks with only 2 video cards installed.

I've tried running the system with just one video card in each of the 3 pci-e x16 slots while all 12GB of ram are installed, no problems there either. So it doesn't look like a defective slot issue.

I've tried running all default settings for cpu/memory speed and timings, as well as manually setting them to what they're supposed to run at. I've manually set memory voltage to 1.65 like it's supposed to run at. I've also tried the previous BIOS to the most recent one, no change in symptoms.

Anyone have any suggestions as to where to look next? I'm hesitant to say it's a bad motherboard, considering that the features do work right, just not all simultaneously....

Full specs are as follows:
i7 965 with TRUE 120
Asus P6T
2x Corsair Dominator TR3X6G1600C8D (12GB total)
3x EVGA GTX 285
Corsair HX1000 PSU
Silverstone TJ10 case
4x Western Digital 300GB Velociraptor
Asus DVD-RW
LG BD-Rom/DVD-RW
Windows 7 Ultimate 64bit
 
nm

I've never tried 6 sticks of ram but mine also runs fine with 3 sticks and 3 cards (not SLI though, just SLI + physix)
 
Lol, well, thanks for the effort. Just for additional testing, i tried all three cards independently in each slot, to see if it was a matter of one card being stupid, but they all test fine independently.

Also, i timed test 1 in memtest, it takes roughly 6 seconds with only 2 cards installed, but 48 seconds when all 3 are installed. I've also noticed the tests run at normal speed until the last segment of each test. So it looks like it's having an addressing problem, however, it's not for a static value. It's always slow on only the last segment of each test. Just plain weird...
 
Have you tried updating your BIOS to the latest version?

Also, have you tried running everything at stock just in case it has something to do with your OC?
 
Doesn't your motherboard have only 2 16 pcie 2.0 slots and 1 4 pcie 4.0? Mine had two blue and one white for pci slots... P6T plain
 
Yeah, I've tried the two most recent BIOS and had the same results. Results are the same regardless of clock speed, currently everything is running at auto, so memory is only at 1066. The third pci-e slot is only 4x, but that should have no impact on this, seeing as the board is marketed for 3 way sli, includes the bridge, and also works fine in 3 way as long as no more than 3 sticks of ram are used. Also, running just a single card in the 4x speed x16 slot works just fine, so I feel confident in saying that's not the issue.
 
What games do you play and how much of an increase is the third card? I've been thinking about picking up a third GTX 480 in the future but dunno what the gains would be like since I was sold on the top end motherboards that have 16x16x16 pcie slots....
 
Usually the gains are moderate at high resolution, but it varies greatly from one game engine to another. There are lots of reviews out there comparing 2 way to 3 way sli. I'd like to keep this thread on topic however, as this problem just doesn't make any sense :confused:
 
Well, still haven't found any answers, so the board is getting RMA'd back to Newegg. Might try the EVGA FTW3 this time and see how that goes....
 
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