Possible to pass through GPU to VM if there is only 1 in the server?


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Hi there,

 

Does anybody know if it's possible to pass through a Nvidia GPU if there is only one GPU in an Unraid server?

I'm using unraid for several months now and im loving it so far, i haven't tried GPU passthrough yet but i remember reading somewhere if you have a server with a CPU without a integrated GPU you have to have a GPU for unraid and you can only pass through a 2ng GPU to a VM.

There is 1 GPU (Nvidia GT710) in my current server, its still in there only because i used it while installing unraid so i never use it.

At the moment there is a AMD 1700 in my server but i already have new hardware like an AMD 3900X and an Asus TUF X570 mobo.

My current mobo is a gigabyte x470 aorus ultra gaming wich had 3 full length PCI-E slots, enough to accommodate my Intel 10Bg nic and 2 GPU's.

My new mobo, the Asus TUF X570 only has 2 full length full PCI-E slots, i can still send it back to the store.

So this is the reason for my question, if you need a GPU for Unraid and a 2nd GPU to pass through to a VM my new mobo can't accommodate that.

 

The reason for the passthrough is because i want to start using the VM as my main (gaming) pc in the livingroom so i can ditch my current gaming pc wich is physically in my licing room.

The Unraid server is behind the wall in the closet where my gaming pc is so its much better if i have the main PC as a VM in the Unraid server.
Im planning to use an 1080Ti (or ill buy a 2080Ti) as passthrough GPU for this VM.

 

Side note, i have triend my new 3900X in the older X470 mobo (with latest F50 bios) but the PC didn't boot.

I should work, maybe i was to fast and didnt give the system time to reboot a few times.

If it should work in the older X470 board, should i just stick the 3900X in that board and dont bother at all buying a X570 board?

I dont have any stuff that can take advantage of the PCI-E 4 speeds, mabe an NVME SSD in the future?

 

Any thoughts are welcome and thanks.

 

Rgds,
Marty

 

Edited by Martyzzz
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10 minutes ago, Martyzzz said:

Does anybody know if it's possible to pass through a Nvidia GPU if there is only one GPU in an Unraid server?

I'm using unraid for several months now and im loving it so far, i haven't tried GPU passthrough yet but i remember reading somewhere if you have a server with a CPU without a integrated GPU you have to have a GPU for unraid and you can only pass through a 2ng GPU to a VM.

Possible without guarantee.

 

You misunderstood odds vs guarantee

Having a GPU for Unraid to boot with improves your odds (i.e. probability) of avoiding problems passing through the (other) GPU.

  • It is NOT a guarantee that you will have NO problem at all (or that it is even possible)
  • Conversely, it does NOT mean that it is IMPOSSIBLE to pass through the only / primary GPU.

Note that dumping vbios does require a 2nd GPU for Unraid to boot with (so you can dump the vbios for the other card) but once dumped, it does not require the 2nd GPU to use the vbios file.

 

Having said the above, I recommend you have a look at the owner's manual of your prospective motherboard to check if its BIOS settings allow you to pick any PCIe slot to boot with (the primary slot). That gives you the flexibility to go the Unraid GPU route without sacrificing the 1st PCIe slot (which is usually the fastest with best clearance for multi-slot GPU).

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1 hour ago, testdasi said:

Having said the above, I recommend you have a look at the owner's manual of your prospective motherboard to check if its BIOS settings allow you to pick any PCIe slot to boot with (the primary slot). That gives you the flexibility to go the Unraid GPU route without sacrificing the 1st PCIe slot (which is usually the fastest with best clearance for multi-slot GPU).

 

Thanks for the reply.

What do u mean by checking if the new Asus X570 TUF mobo supports any PCI-E slot to boot with?

I dont mind (if a 1st GPU is needed to pass a 2nd GPU through to a VM) if its slot 1, 2 or 3 because all slots have enough clearance.

It's just that i never use the Unraid GUI so therefore (and also to save power) i have no need for a first "unraid cheap GPU" and i just want to run a powerfull GPU to pass through to a VM.

Thing is i cant test it atm because i have no 2nd (powerfull) GPU available atm so i want to be sure if my new mobo (with only 2 PCI-E lanes) will be enough.

 

Rgds,

Marty

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15 minutes ago, Martyzzz said:

Thanks for the reply.

What do u mean by checking if the new Asus X570 TUF mobo supports any PCI-E slot to boot with?

I dont mind (if a 1st GPU is needed to pass a 2nd GPU through to a VM) if its slot 1, 2 or 3 because all slots have enough clearance.

It's just that i never use the Unraid GUI so therefore (and also to save power) i have no need for a first "unraid cheap GPU" and i just want to run a powerfull GPU to pass through to a VM.

Thing is i cant test it atm because i have no 2nd (powerfull) GPU available atm so i want to be sure if my new mobo (with only 2 PCI-E lanes) will be enough.

Read through the manual pdf. Find out if the BIOS says anything like "Initial display output" or "Primary display output" or something like that.

Having a skim through the pdf on Asus website, I don't think it has that (in fact, it looks surprisingly quite limited - I can't even find PCIe bifurcation but then I skim).

 

PCIe slots are not all the same. And don't confuse "lane" with "slot". A x16 slot can only have x4 lanes.

The 2nd PCIe x16 slot on your X570 motherboard only supports up to PCIe x4 speed (i.e. lanes) which, depending on the GPU, can be too slow.

If the BIOS allows you to pick the slow slot as primary display then you can put a cheap GPU on that slot to boot Unraid with (e.g. a GT 710) and have your powerful GPU to pass through.

 

You seem to misunderstand what the 2nd ("Unraid") GPU is used for. It doesn't matter if you have never used the Unraid GUI.

Having a GPU for Unraid is less a requirement for Unraid but rather to stop the other (main / powerful) Nvidia GPU from booting up (so to speak) so that when it's passed through to the VM, it is less likely to detect that it is being used in a VM and thus doesn't throw error code 43.

It also makes things easier to dump vbios etc.

 

Again, there is no guarantee. You can only have 1 GPU and pass it through fine without error code 43 and vice versa may have 2 GPU and have the problem.

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Cheers again for the reply !

I wouldn't stick a beefy GPU in any other slot then the top one, just be sure.

As i not 100% convinced I can use 2 GPU's and 1 NIC that require 3 full length slots so I decided to return the TUF mobo and ordered a Asus Strix X570 gaming wich does have 3 full length slots.

 

Rgds

 

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  • 6 months later...
On 12/10/2019 at 1:28 PM, Martyzzz said:

Cheers again for the reply !

I wouldn't stick a beefy GPU in any other slot then the top one, just be sure.

As i not 100% convinced I can use 2 GPU's and 1 NIC that require 3 full length slots so I decided to return the TUF mobo and ordered a Asus Strix X570 gaming wich does have 3 full length slots.

 

Rgds

 

How did it go with the Asus TUF X570 Mobo and the GPU passthrough?

I've got a Asus TUF X570 coming to me soon and am curious about your experience. Can you confirm this Mobo completely eats up a GPU in order to boot....and that it actually forcefully eats the primary PCIe x16 slot too!?

Edited by Stupifier
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  • 3 weeks later...

Hello, 

did you manage to get everything running with the Asus Tuf X570 Gaming Mobo. 
I am struggling to figure out how to boot into unraid from the second graphics card GT 710 in order to make passthrough with my RTX 2080 which is located in the first PCIe slot. 
Is a second card required or would unraid switch the video into the VM when booting it?  

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  • 1 year later...
8 minutes ago, Bern8 said:

did you manage to get it working with the Asus Tuf X570 + RTX 2080. My screen turns just black when booking from the VM. 

VNC boot works. Also got the modified vbios and followed various Spaceinvader videos. Used Seabios, QM35. 

 

I have an asus mb too and an nvidia gpu, uefi and legacy bios compatible; I converted a couple of days ago a kali linux vmdk to qemu/kvm+libvirt and since it wasn't created with an efi partition the boot was with seabios: with this configuration there was no luck to passthrough the nvdia gpu: black screen.

Just converted the vm to boot with ovmf (uefi) and it just worked.

First thing I would do is to setup the vm as ovmf+q35: if you still have a black screen post your diagnostics file and the output of the command "cat /proc/iomem"

First one is needed to look at your hardware, type and addresses, xml of the vm, errors in log files, the output of cat is needed to look if the gpu is used by something else that needs to be disabled (usually efifb with unraid uefi boot and a single gpu).

You can just search in this subforum, I replied several times about this and solutions.

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