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NVidia Passthrough with Dual Monitors

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I wanted to make sure this information was posted somewhere being that I really haven't seen much about dual monitors and even less when it comes to dual monitors on NVidia cards.  There is a thread I found with fixes posted for AMD cards, but even that is a year old.


Anyway, my findings......  I have an Unraid server with 3 VMs on it.  2 of the VMs have passed through video cards, all of which are NVidia.  I have an EVGA 1080ti, MSI GTX960 and a Gigabyte GTX960.  Trying all combinations between Windows 10 and MacOS, I get the same results when trying to connect two monitors/displays to the same video card in an OS.  Neither OS will boot with 2 displays connected.  I have to boot both OSes with only a single display connected.

Once booted to the desktop, if I plugin a 2nd display in either OS via HDMI cable or DVI adapter to HDMI cable, I get flickering displays, snow on and off on either/both displays and sometimes both displays will go completely blank.  If I pull 1 or both HDMI cables, wait a few seconds and connect 1 at a time, sometimes I can get a full dual display working.

Even if I get it working, if I were to change from extended desktop to mirror display or vice versa, I go through the same blinking, flickering, on/off, etc. and have to play with cables again to get it working.  Sometimes the video card output will just give up and not output any display.  The underlying OS is still running because I can connect to it with screensharing or NoMachine and access the OS, but the video card stops output any data.  The only way to fix this scenario is to fully shutdown the bare metal machine and then power it back on.  Even a reboot won't reset the video card to get output.

I have gone a little further in my testing to determine that the likely cause is Unraid.  If I boot Win10 and MacOS, both with single displays, each on their own card and own monitor.  Everything works just great.  I then found AirDisplay by Avatron that will allow a Mac to extend it's desktop onto a Windows PC via a screensharing type method.  A client runs on Windows as an app and receives the signal from the Mac.  On Windows, you can resize the window as you please or set it to fullscreen and on the Mac you can use this as a Mirror display or extended desktop.  When trying out AirDisplay, I get the same results as if I used the physical video card and tried to connect 2 physical displays to the same video card again.  This leads me to believe it's an Unraid issue.

While I am pretty technical, I have not had to do much troubleshooting with Unraid and don't know for sure which files/logs would be of use to developers.  I can send along my logs if necessary, but I am also running out of free time to test these things at this point, being that I have been setting up and configuring my Unraid machine for about 3-4 weeks now to use it as my daily driver desktop and gaming machine.  I am able to do some more testing and post up some log files, but making major changes to anything underlying that could cause corruption or downtime on my system at this point isn't too likely.

I'm posting everything here to pass along as much information as I can and multiple scenarios.  Hopefully someone else has had similar experiences and can confirm what I have found at this point and hopefully this is something that can get straightened at some point in the near future.  It would be great to get my dual displays back on MacOS as that's what I use the most and what I use as my daily machine. 

I am using a work around at the moment of ShareMouse to use a single keyboard and mouse between both OSes so that I can at least make some use of my 2nd display by browsing the net in Chrome on Windows, doing some file transfers and other common items between OSes.  It works and is helpful, but definitely not dual displays on the same OS.

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I run 2 gpus with dual monitors in a single workstation without issues. And i'm sure i'm no the only one.


Weird question, but Is your power supply big enough to support running 3 gpu's?


Without posting your diagnostics after tying to start the vm's, you may not get much help unless someone ran into this specific issue and resolved it.

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Although AMD, I also run dual output VM's without any issues or workarounds. 

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Ditto.  I've got 2 monitors running off my humble GT 730, and 2 VMs running off GT 710s all concurrently with no problems.

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Hmm, ok.


1812, I did specifically say that I wasn't sure what files needed to be posted for diagnostic help.  I did not go looking to find out what I had to upload as I posted that message last night before I quit for the night and today I'm on the road and won't be able to access my unraid server for testing until the end of the week.


I do indeed have a large enough power supply.  It's 1000 watt which is more than sufficient for the hardware I have installed.


I should also mention that the Win10 OS did boot previously on v6.4 rc15e with the EVGA 1080ti and the Gigabyte 960 at the same time.  I had not tried again until the other day as my main goal is to get 2 displays working in MacOS.  I really don't need the 2nd GTX 960 in the machine, I installed it for testing purposes as the other cards will certainly power 2 displays easily for my use.


DZMM has 2 displays on a GT 730.  Saarg is on AMD cards.  1812, what cards are you using?  Just curious if it's something with the newer cards, higher end cards, etc.  Like I said, Windows did boot and operate with two cards a few versions back and I just remembered that as I was reading info today.


If I have time this weekend, I will try some older versions of unraid 6.4 RC.

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2 hours ago, ckoepf said:

1812, what cards are you using? 


one box has a gt710 and a gt730 both with dual monitors.

another box I have has a gtx 1050 and gtx 1060 both running dual monitors on an a single osx vm.


both are running on 6.4 rc either 19 or 20.


depending on how you set up an osx vm (and what version), sometimes it may not show you a boot screen until the vm is in the final stages of booting right before the desktop loads. Also, there was a version of clover/nvidia drivers that had issues and only showed a black screen if you had display port plugged monitor plugged in during boot.

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So that's some info for me.  OSX is on High Sierra.  Are you running Sierra?

I have tried various version of Clover and have also left it sit after start up. 


That still doesn't explain what happened with Windows 10.  As I said, I was only trying the dual displays on Win10 for testing purposes to see whether my problem is OSX or something more general.  Win10 was working and now doesn't.  The only change was the update to the later 6.4 rc.


I had thought about creating an OSX Sierra installation to see whether that would work to determine if it's the NVidia Web drivers or something else.


I will also have to looks at the logs to see if I can find something in there too.


Unfortunately, no testing until this weekend and even then, time is a little short.  

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All my OS X vm's are Sierra 10.12.4 using Nvidia web driver 378.05.05.05f02. 


I haven't messed with High Sierra yet as I'm waiting on it to appear to stabilize in terms of virtualization. Then I'll begin the process (maybe this summer) of updating each vm instance.


with windows 10 not working either makes me think there is something at the system level causing your issues. when you have time, post tools>diagnostics zip so we can see what you're working on.

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When I started setting up my virtualized OSX, my Macbook Pro was already on High Sierra.  If i had known the situation, I probably would have stayed on Sierra.


I will post the diagnostics later this week when I'm back home.


Another thread you commented in about bios settings has me wondering if I could change some PCI settings in the bios that would have an affect on this.  I have to look what settings are available though.

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Posted (edited)

*EDIT* I will start a new thread since this is in a deprecated forum.


Sorry to necro this thread, but I am having a very similar problem right now that I'm trying to figure out. I am passing through a GTX 1050 to a Windows 10 VM. Physically connected are two 4k LG TVs mirrored via HDMI. This was working perfectly for months (since December) but I've recently started experiencing issues where the TV downstairs is not detected no matter what I do (the upstairs TV works fine). After reading this thread and @ckoepf's technique I learned that I can turn off the VM, disconnect both HDMI cables, turn on the VM, wait for the OS to load, then connect one hdmi cable at a time. This will make the VM recognize both displays until it's rebooted, then it goes back to only detecting the upstairs TV.


There have been no changes on the VM, but unfortunately I have made several changes on the Unraid side which are listed below:

1. I connected a USB cable to my TrippLite UPS and started the apcupsd daemon. (We recently had an extended power outage which drained the UPS and caused the Unraid server to power off unclean.)

2. I upgraded to Unraid 6.8.3 from 6.8.2

3. I installed an old WinTV-HVR-2250 tuner card in the PCI slot next to the video card so that we could watch OTA channels for local news broadcasts. This also required me to install the "Unraid DVB" plugin so that I could load a custom image (LibreELEC 6.8.3) that contained the drivers for this card. And finally TVHeadend Docker container.


I have since reverted the changes in point 3 thinking that was causing the issue (Removed the tuner card, reverted back to vanilla Unraid 6.8.3, Stopped the TVHeadend docker), but no dice.


@ckoepf were you able to find a solution?


Edited by Hoof

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