Any problem running unRAID flash off of a PCI USB 2.0 card?

[De1taE1even]

Hey all, I was trying to get a USB bus forwarded to a Windows VM on my backup server, but I'm having issues.  My AsRock mobo only has 1 useable usb bus, so I can't forward it to my VM, since my unRAID flash has to utilize usb.  I tried everything, including overriding ACS.  My mobo's BIOS settings didn't help either.  From the research I've done, it's actually not AsRock's fault.  The H97 chipset is to blame evidently.  If you want to utilize both usb 2.0 and 3.0 ports, the chipset automatically uses EHCI for all ports.  There is evidently no way to force the mobo to use XHCI for 2.0 and EHCI for 3.0.  That scenario simply isn't supported by the chipset.  So, I don't know of a way around it.

 

I searched around the forum a bit, and popular suggestion was to add a pcie usb card and forward that to the VM.  Great!  I even have one of those cards laying around!  Well, I thought it was great until I realized I don't have an open pcie slot in my mobo!  The only open slot I have in the mobo is an old-school PCI slot, which brings me to the question in the subject line.

 

Is there any problem buying a PCI USB 2.0 card, and running the unRAID flash drive off of it, so that I can forward the EHCI bus to the VM?

 

Thanks.

[scorcho99]

I seem to remember that KVM passthrough doesn't have support for plain old/legacy PCI device passthrough. I saw it in a forum somewhere and thought it was a bummer. It is possible to do, ESXi does it. All devices under a PCI bridge must go together which in practice almost always means every PCI slot must go to the same VM...but it is possible and does work on ESXi. But for whatever reason, KVM decided not to implement it. I can understand why, its of much more limited use than pci-e passthrough. Maybe things have changed though or unraid is better about this?

[De1taE1even]

Sorry, maybe you misunderstood my question. Since I only have one USB bus, I was thinking about installing a legacy pci USB card to run unRAID off of, so that I can pass through my one USB bus to the VM. The legacy pci bus wouldn't get passed through. I was just wondering if I'd be asking for trouble by running unRAID off of a legacy pci-usb card.

[scorcho99]

Sure. The problem you'll run into is that you can't usually boot off an add-on card USB port, I think it would need its own boot option ROM which I've never seen one have. You CAN get around this though, if you're willing to endure extra slow unraid boot.

Here's what try I'd do:

1) Buy a cheap VIA USB2 PCI card with 5 ports (I only suggest this card because I've used this particular kind of card like this before)

2) Install plop boot manager onto a bootable USB flash drive

3) Plug that flash drive into the motherboard USB ports

4) Install the PCI card, plug Unraid into that

5) Configure bios boot from the plop boot flash drive

6) Once plop manager comes up, configure it to ignore its own device and then tell it to boot from USB

7) Unraid should now boot, brutally slow, but it should boot.

Now you can passthrough the onboard USB controller to another VM

 

Unnecessarily following up on my first idea, I googled around and it looks like legacy PCI passthrough is deprecated and now unsupported but I think it can be enabled. I've never heard of anyone doing it myself with KVM.

[De1taE1even]

Ah, gotcha.  Didn't think about that.  I was more worried about it from a system stability standpoint, but I didn't even think about having trouble booting from that card.  Thanks for the info!