That is part of a question I also have - when I have 2 GPUs
One for the boot screen and one for after.
How do I change in the OS X after booting?
Or I just remove the video cable of the monitor and move it to the other card and this enables the second GPU?
May be a simple cheap display port mechanical switch can do the job.
Pull the cable is one of the option, but I don't think it's a good idea to do that everyday, or even few times per day.
Some monitor has multiple input, you may use the monitor input selector as a solution. However, the Mac will consider you are connecting to 2 monitors. You can choose the mirror option to avoid the mouse cursor going to the "offline" monitor, but I am not sure if the GT120 will affect the overall system performance in this case.
With a switch, you can easily switch the online / offline GPU. The system won't consider you are running multiple display, and you can put the switch right next to you, no need to reach the back of the Mac Pro. And less chance to induce any damage (pulling a cable that is transmitting usually is not a good idea.
Correct, but the OP said a 1080ti, that's a different story. The ti, very well may need external power:
http://www.macvidcards.com/blog/the-pesky-power-issue-with-pascal-1080ti-and-titan
Lou
My bad, I misread that. Thanks for pointing that out. However, 1080Ti is virtually the same situation.
I am running a 1080Ti right now. I can confirm that CUDA-Z heavy test can cause issue. However, that seems to be a very exceptional case. Even MVC page stated that, the power draw of the 1080Ti is generally lower than the 980Ti, and the 980Ti can run with just the mini 6pin.
I can run everything including Furmark (and OCCT in Windows) without any issue. And obviously the power draw for real world usage is not a problem at all. I tested it in both MacOS and Windows.
So, unless OP get a factory OC 1080Ti. Or his daily job is to run CUDA-Z heavy test. IMO, there is no need to go through the pixlas mod. But of course, if he doesn't mind to do that, I totally agree that let the 1080Ti drawing power directly from the PSU is better than via those tiny mini 6pin ports.
Anyway, even if don't want to go Pixlas mod, and worry about the power draw, as MVC said, a simple SATA to 6pin cable can also alleviate the problem. Not really need an external power.
