I have dual gtx 960s running 6 monitors, 3 each.  I had to use the 
nouveau open source driver to put everything in 1 xscreen.  If your 
using the nvidia propriety driver, it has an artificial limit of 3 
monitors per xscreen. They do this to force power/pros to go with their 
quadra line which doesn't have the limit. I have run this setup 
successfully for 2 years, but on Fedora.  I'm running F28 right now, 
with KDE.


On 08/27/2018 09:57 AM, Andrew Lunn wrote:
> On Mon, Aug 27, 2018 at 09:29:40AM -0500, o1bigtenor wrote:
>> On Mon, Aug 27, 2018 at 8:44 AM, Andrew Lunn <andrew at lunn.ch> wrote:
>>>> Running as previously, on Debian testing (10 or buster) with a pile of
>>>> ram and and (lots of resources), with what may be more unusual is 2
>>>> graphics cards and 4 monitors set up as 2 x-screens. (Would love to
>>>> condense that into 1 screen if someone has the know how and can
>>>> describe it but 2 works well enough even if 1 would be quite slick
>>>> (and very 'interesting').)
>>>
>>> Are the two cards from the same vendor? Or different vendors?
>>
>> Both are nvidia 570 cards from the same vendor.
>>>
>>> I've done this in the past using Xinerama.
>>
>> I am using xinerama but using 2 xscreens. Its using only 1 xscreen that
>> I don't know anything about!
> 
> You should not need to use Xinerama in order to have one Xserver merge
> two screens on a single card.
> 
> Ah, hold on. Are you using the proprietary nvidia driver? Maybe you
> have to use Xinerama for that driver?
> 
> All the open source drivers should drive two displays on one card
> without any additional configuration.
> 
> You might also find the open source driver just correctly finds two
> cards, four displays, and it all just works out of the box.
> 
> But there is a trade off. The open source drivers might just work out
> of the box, the nvidia proprietary stuff will give you better
> performance. If it is a gaming machine, you probably want the
> performance. If its just a developers box, where you just need large
> screen acreage, mostly text, the open source driver might be
> sufficient.
> 
>      Andrew
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