Fri May 12, 2017 5:18 pm
There's not a hard answer.
Generally on Mac, 3 high end GPU's is the limit. But some people seem to be able to have more. It depends somewhat on what OS version and what type of cards are used. Generally, on El Cap or Sierra, if you go over the limit, the system won't boot. If it boots, it's probably going to see all the cards. You can verify in About This Mac - System Report - Graphics/Displays. If all the GPUs are properly identified, then Resolve should be able to see them and use them. You can verify that in Resolve Preferences - System.
On Windows 10, we have in the past recommended a 3 GPU limit. However, I've seen people with more. Up to 7, in fact. But there could be stability issues with that many. So again, it's a "your mileage may vary" type of situation.
V14 may make the Windows situation better with multiple GPUs, but the development team has not yet provided specific guidance on that. Hopefully by V14 release time, we'll have a better idea.
Dwaine Maggart
Blackmagic Design DaVinci Support