Two graphics cards means PCI x16+x4?

[AndreeOnline]

Those of you running two gfx cards in a Mac Pro, are you putting the cards together in the lower x16 slots, or are you leaving some space for airflow and putting the top card in one of the x4 slots?

Are there any benchmarks for this?

If both cards end up in the lower x16 slots there will be very little room between them for air...

 

[mikeboss]

it depends. do you intend to connect a display to the 2nd card or will you just use it to accelerate rendering? if you use the 2nd card to accelerate, let's say FCPX, you won't notice if the card is in one of the upper two slots.

 

[AndreeOnline]

Those are my exact thoughts...

I currently use a non flashed R9 280X to drive two Dell 25" 2560x1440 panels.

Either I add another identical card (to support FCPX and DaVinci—no gaming), or I buy two new cards—more powerful still—with the same basic setup: one card to drive displays (and help with rendering as much as possible), and the second card is then strictly for compute.

I have a hard time estimating what the impact would be in DaVinci (as an example) where both cards are used almost to 100% to put pixels on the screen in real time. It isn't just rendering/calculating in the background.

 

[mikeboss]

just plug the card you're currently using in one of the upper two slots and you'll know about the impact it has

 

[AndreeOnline]

Hehe… true… =)

But you know... the road of least resistance... sometimes you learn that it's already been tested.

Should ask Barefeats.com He has done a lot of dual GPU tests.

 

[mikeboss]

of course, this has been tested already. but I can't remeber who/where. AFAIR people were surprised about how little the impact was.

 

[IowaLynn]

Those of you running two gfx cards in a Mac Pro, are you putting the cards together in the lower x16 slots, or are you leaving some space for airflow and putting the top card in one of the x4 slots?

Are there any benchmarks for this?

If both cards end up in the lower x16 slots there will be very little room between them for air...

I see PC setups in boards like eVGA with 2 and 3 double width cards, so it should be fine with proper cooling and fan speed but then you can no it or GPU Yen and even adjust graphic card can speed.

There are no utilities to monitor and control fans and GPU temp in Mac OS?

 

[matthewtoney]

Those of you running two gfx cards in a Mac Pro, are you putting the cards together in the lower x16 slots, or are you leaving some space for airflow and putting the top card in one of the x4 slots?

Are there any benchmarks for this?

If both cards end up in the lower x16 slots there will be very little room between them for air...

True enough, although I suppose the particular cards in question and how hot they run at idle and under load makes a big difference. I'm doing this running 2 GTX 970's and they are in the bottom 2 x16 slots - even under prolonged heavy load they don't seem to have any problem at all managing the temp and using the fans to keep them cool. These 970 cards must run fairly low temp to begin with tho. When I first put them in it really weirded me out when I booted it up and started testing things and the dual fans on both cards (neither are ref designs) stayed completely off until they were under heavy load for some period of time. The cards came with a notice tucked in the box about just that though - said to basically not freak out since at idle and normal usage the fans on these cards would not run at all. (and it was right - they don't)

 

[AndreeOnline]

Cool. Literally. =)

Are nvidias plug and play these days?

Was it a seamless install for you? What brand do you use?

I know there are some 4k60Hz issues, right? I currently use a 280X to drive two 2560x1440 screens without issues.

 

[matthewtoney]

Cool. Literally. =)

Are nvidias plug and play these days?

Was it a seamless install for you? What brand do you use?

I know there are some 4k60Hz issues, right? I currently use a 280X to drive two 2560x1440 screens without issues.

Plug and play? Yes, but with caveats:

For GTX 970/980 and other maxwell based Nvidia cards they only work with Yosemite and *with* the Nvidia web driver. The driver builtin to Yosemite unfortunately is based on an older revision (310.X) so it gets tricky to do OSX updates since if your system gets reset back to using the builtin driver all you will see is a black screen. However, Nvidia has a new driver revision ready usually darn quickly so I personally find it manageable, plus I have an older GT120 card here that I swap in if I ever need to in place of one of the 970's in order to boot a default OSX install and re-install drivers, etc.

Others will have to answer the 4k questions, although my understanding is that its mainly about combining it with a 4k monitor that can do 60hz via SST if you're using Nvidia - I am *now* an expert on that though so I could be totally off on that. (I run 4 screens myself, but they are 2560X1600, 2560X1440, 2560X1080 and 1080X1920 - no 4k upgrades for me right now)