Just wanted to share my experience as I was trying to virtualize Unraid using Proxmox. 

 

TLDR:

1. Try to find a motherboard which has a separate SATA controller not present on the same IOMMU group.
2. If you face an issue where your Unraid USB stick is not bootable, migrate it to a new one.

I already was running Unraid bare metal  on my low power "server". I wanted to upgrade my Unraid server to intel 10400 and then use Proxmox on it. I understand Unraid can also be used as a Hypervisor. However, Proxmox is better in regards to performance, backups and other features for a Hypervisor. So that was my plan. My Unraid setup was not very elaborate. Only 2 16TB disks with only shares. No extra plugins. I might use some in future.

Reading up on the internet I got the impression that it can be done and is very simple as Unraid is primarily stored on USB and doesn't care much with hardware differences.
So I built the new server and installed Proxmox on it on a 1TB Gen3 SSD. Did the required essentials to passthrough existing disks (Yes individual disks as I was not using a controller board. Only existing 6 SATA ports on the motherboard.). Next added a passthrough for my existing Unraid USB, a USB2.0 16GB Sandisk Cruzer Force. Now the issues I faces:

 

1. Proxmox complained that the device isn't bootable. Changed the bios to UEFI on proxmox. It still didn't got recognised as a bootable drive. What finally helped me was running Unraid bare metal on new server. Creating a backup and then using a new USB stick with the Backup flashed. I used a USB2.0 Sandisk Cruzer Blade. This worked flawlessly. . This was very weird and took a lot of time to figure out. I was already using UEFI mode. I could see the folder EFI under my USB root.  If anyone has any ideas why would this be, please let me know.
2. To my surprise, Proxmox doesn't actually passthrough disks. It showed up on Unraid as a QEMU disk which Unraid didn't recognise as a part of existing Array.
   I again read up online regarding this and found out generally people successfully using Unraid on Proxmox passthrough entire PCIE SATA controller. In my country, these are very expensive. And, I couldn't just wipe the disk as I didn't have any other form of high storage. Reading further online lead me to passing onboard SATA controller to Unraid. However, people did mention some weird issues with Controller not resetting rendering it useless for VM. Luckily that didn't happen to me. I could see an Intel SATA controller upon running lspci.
   I got lucky! Or maybe not. Might face some issues in the future. I have one more M.2 nvme slot present. So it should be fine if I am not able to use other SATA port for SSD.

 

So if you plan to Virtualize Unraid. Keep this i mind. Try to find a motherboard which have a separate SATA controller not present on the same IOMMU group. I was using Asrock B560 ATX motherboard.

Edited May 15, 20233 yr by aditya333
mistake\

Well I haven't even gotten to the stage of trying to passthrough disks and/or controllers. I'm still trying to get the thing to boot. So far I have done the following:

 

1. Updated both the firmware and BIOS on my motherboard to the latest

2. Flashed 6 different USB drives with the UEFI option turned on and off and attempted to boot in both legacy and UEFI mode

3. Tried booting on bare metal

4. Tried booting in a Proxmox VM

5. Tried booting on an entirely different machine

 

All I get is the looping countdown from 5 to 1 then back to 5 again. Troubleshooting continues.

In my case to get USB working to boot unraid as a Proxmox VM I needed to move the USB drive to another port on the server, as in the first one I don't know why, was refusing to recognize the passthrough USB as bootable device on the VM. Ended installing the USB drive on an interior port on the server. Now works without problem.