Video Card pass-thru confusion

[SWKerr]

Noob to unRAID!  Setup first server this weekend and have some questions related to passing thru a video card to a Windows 10 VM.

 

Setup:

Ryzen 1700 with a MSI B350M Mortar motherboard and 16GB RAM.

3x4TB, 1x3TB Array with Parity, 512GB SSD Cache drive

MSI Radeon RX 570 ARMOR video card (Also: using a AMD HD6450)

 

The setup has been pretty painless and the Array is working well with excellent performance.

I was able to setup a Windows 10 VM with VNC\Remote Desktop with out issue.

But:  I want to pass-thru the video card to to the VM so I can get gaming level performance while also running the unRAID file server and maybe some dockers.

And here is where I am having a problem.

 

In researching unRAID, everything I saw indicated I needed to have two video cards.  
One for the unRAID server and another for the VM.  (Ryzen does not have built in graphics, added a HD6450)

The primary issue I have is that unless the card is in the Primary video slot it will not get its own IOMMU group.
So I can not pass-thru a video card that is not the boot screen card without an error.

 

Now here is my confusion.  

I can boot with only the RX570 and then assign that card to the Windows VM from the Dashboard.

I have to use another PC or cell phone\tablet to start the Array and VM but it appears to work when started without impacting the server.  

When I start the VM the screen goes blank for a few minutes while the VM boots but then it seems to behave normally.

From the videos I have seen and the reading I did I did not think this would work.

Is there a major downside to doing this or is it pure luck that it works?

Honestly this seem easier than the steps in most of the guides I have seen.  

 

Also: 

I would like to figure out if it would be possible to get a second video card working.

I have turned on "Enable PCIe ACS Override" but it does little to break out the IOMMU groups.  

Is this related to the newness of the Ryzen motherboards or is there something that can be done manually with the xml file to pass-thru the cards or other hardware not in their own group?       

 

Edited June 13, 2017 by SWKerr

[Tuftuf]

Good thread to read is                    Anybody planning a Ryzen build?                 

 

Many have needed to disable Global C State to have a stable system, there is more info in the thread.

Personally I need to keep Enable PCIe ACS Override on even though my GPU is in it's own group or I have additional audio issues (on top of the minor one I'm still having).

 

Yes passing through your Primary works, this works better with AMD cards than Nvidia but there is a workaround for Nivida. I sometimes get the black screen and first thing I see is windows login other times I see the bios.