I know the title has 2 likely red flags (USB and virtual) 
I found several related and very similar discussions but didn’t see this exact scenario. Please link me to the answer if it’s been addressed.
Q: For connecting a single disk pool to a virtualized TrueNAS Core, is passing the USB device from the hypervisor (Proxmox VE 8.3) to the VM a no no? If so, would PCIe passthrough of the USB controller be a reasonable method for connecting/importing an offline backup pool?
Background: I am trying to find an acceptable setup for infrequent backup of certain datasets to a single external disk. I have been using a virtual TrueNAS core vm on proxmox that accesses its disks through an HBA in IT mode that has been passed through to the VM. My first plan after reading the resource by @Arwen was to put my external drive in an enclosure with eSATA and connect it to the same HBA card. I’ve been struggling to find a reasonably priced product that has ventilation and eSATA. A no-fan cheap StarTech product I tested briefly severely overheated in the first hour. The only proper option seems to be Cru RTX110-3Q which is way too expensive (especially after customs and shipping for me). So I’m thinking I should experiment with USB enclosure first before biting the bullet and getting something like that. I am able to pass through a USB controller but 2 of 4 USB ports on my server become dedicated to TrueNAS which is not ideal for my other VMs, hence the 1st question. (I know it would be best to separate the NAS from this server entirely but that’s not immediately possible.)
Thanks
I mean… I wouldn’t do it - any of it personally. I was going to recommend going for passing through the controller to make the best of a bad situation, but you mentioned that you have need of the ports it services. for other VMs.
Since you have some sort of enclosure with eSATA, any chance you can just slap a fan onto (or facing towards) that enclosure so things don’t overheat? That to me seems like the most palatable option.
I’m assuming this is a temporary thing for a backup that you can keep in cold storage, so a janky fan pointing pointing at the enclosure won’t drive you crazy?
Thanks. My new ironwolf disk reached 61 degrees in an hour while doing a long test, I aborted it and took it out, added it to the NAS just for testing and disk was fine. I saw some amazon reviewer mentioning how they moded the device to install a tiny fan by cutting the back etc, sounded like a lot of hassle…
Yes I’ll be keeping the disk offline at 20~22 celsius. I prefer not to lose 2 USB ports for this but I can make things work if that’s the only way. (I use Asrock x570D4U too btw), as long as it’s likely to work out OK with TrueNAS. There are many fan-equipped cheap enclosures (e.g. this one I found after searching for the unavailable product of the same brand in the backup resource article). Based on the long list of issues with USB, I suppose the only way for me would be to experiment with the particular enclosure to see how it goes? I have a shallow understanding of how replication tasks work in general. So let’s say the enclosure sometimes acts up; will I always know, i.e. by seeing an error in the task log, if something goes wrong and the backup is corrupted? In that case I could mitigate it by rotating 2 disks.
That is just the cheapest way - but without fully understanding how the enclosure closes - I’d just do my best to get all the wires/connections in place & not have the thing clamshell & then point a fan at it.
Otherwise I’d dremel the crap out of it
Thanks for the feedback. I couldn’t get the USB pass-through to behave as I expected. Asrock Rack X570D4U USB controllers show up in different IOMMU groups so I assumed I had 2 controllers to pass through only 1 of them. But regardless of which one I chose to pass to TrueNAS via the PCIe Device menu in proxmox GUI, all USB devices connected to any other physical USB port became unavailable to use in other VMs. TrueNAS did successfully recognize the USB disk and completed its replication task of course.
I’m still looking to find out why. Though this inconvenient setup for backup plus a couple others is now pushing me to finally separate my NAS and run it on bare metal.
