PCIe USB cards for Proxmox passthrough: controllers, not just ports

A VM with its own USB controller is a handy little island: plug a device into its ports and let the guest handle it. The buying trap is that four USB sockets can hide very different controller layouts. Start with StarTech PEXUSB3S44V for a controller behind each port, or Sonnet Allegro Pro USB-A, USB3-PRO-4P10-E, for four 10Gbps ports you plan to give to one VM.

Specs and setup steps come from the makers, Proxmox and Linux documentation, checked October 26, 2026.

Quick picks: buy the controller layout

• Controller per port: StarTech PEXUSB3S44V. Four Renesas controllers serve four USB-A 5Gbps ports. Choose it when individual port ownership matters more than a 10Gbps socket, or when you need the included low-profile bracket.
• Four faster ports for one guest: Sonnet Allegro Pro USB-A. Two ASMedia ASM3142 controllers serve four USB-A 10Gbps ports. Choose it for a VM with several fast USB peripherals and a full-height slot; the card takes its power from PCIe rather than an extra PSU lead.
• Just one dongle? Try existing USB-device passthrough first. Proxmox can assign a device by vendor/product ID or physical bus/port. You can keep the motherboard controller on the host and skip the expansion card.

A card earns its place when you want the guest to own the physical USB controller, not merely receive one selected device. The Proxmox host USB documentation explains the device-level option.

Compare the hardware before counting sockets

Feature	StarTech PEXUSB3S44V	Sonnet USB3-PRO-4P10-E
Host controllers	Four Renesas/NEC µPD720202	Two ASMedia ASM3142
External ports	Four USB-A, rated 5Gbps each	Four USB-A, rated 10Gbps each
PCIe connection	PCIe 2.0 x4	PCIe 2.0 x4
Bracket / fit	Standard bracket; low-profile bracket included; 16.7cm long	Full-height, half-length card
Auxiliary power	SATA or LP4/Molex; maker recommends connecting one	None; powered by the slot
Maker-rated port power	Up to 900mA / 4.5W for USB 3 devices	Up to 1.5A / 7.5W per port
Best fit	Planning ownership one controller at a time	A whole-card USB setup for one VM

These are interface ratings. Use the StarTech datasheet and Sonnet specification page for the exact models; don’t multiply socket speeds into an expected file-copy result.

StarTech: a useful layout for separating jobs

The PEXUSB3S44V has four host-controller chipsets, rather than one controller with four downstream sockets. That gives you a clear hardware starting point for putting different USB jobs on different controllers. You might want one controller for a guest’s radio and another for a guest’s removable media.

The low-profile bracket also makes this the practical choice for a slim machine, provided the card’s length and x4 slot fit. Connect either SATA or LP4 power as shown in the installation manual. That manual lists Linux support; the passthrough steps come from Proxmox below.

Sonnet: four 10Gbps ports, one-VM plan

The Sonnet is attractive when one guest needs several fast peripherals and you don’t want another power cable inside the case. Its current maker page lists supported Linux kernels from 6.6 onward. It also says booting from the card is unsupported, so leave your host boot drive elsewhere.

Read Sonnet FAQ 1149 with this model: some Linux systems fail to detect attached USB devices. The maker’s documented workaround changes the card bridge’s ACS redirection; when that workaround is used in a virtualized environment, all four USB ports must be assigned to one VM. That’s why this guide picks it for one guest, rather than a split-VM arrangement. The manual points to the Linux note; FAQ 1149 gives the requirement.

The one host check that decides ownership

Your motherboard and chosen slot determine the IOMMU groups: assign a controller separately only when its group can be dedicated without taking a device the host or another VM needs. Four controllers don’t automatically mean four independently assignable guests. Related functions or a PCIe bridge can appear in the group too; inspect every member before deciding.

Linux describes groups as the ownership unit used by VFIO. Proxmox documents the group inventory and notes that moving a card to another slot can change the result. Keep the full platform setup in our Proxmox passthrough guide; the same host-side preparation matters here, without the GPU-specific display settings.

On the Proxmox host, start with these read-only commands:

lspci -nnk
pvesh get /nodes/NODENAME/hardware/pci --pci-class-blacklist ""

Replace NODENAME with the node name shown in your Proxmox interface. Find the USB controllers, their PCI addresses and current drivers in lspci, then review the group membership in the PCI inventory. Compare the inventory before and after installing the card so you can distinguish it from the motherboard’s USB hardware.

Will the card fit your build?

Check the board manual’s electrical slot wiring, not just the length of its plastic connector. Both shortlisted cards use an x4 connection. A long slot may share lanes with an M.2 socket or another expansion slot; our AM5 motherboard guide shows why those lane tables are worth reading.

For the physical shopping list:

• Bracket: StarTech includes a low-profile option; Sonnet specifies full height.
• Clearance: allow room for the card, nearby GPU/HBA and USB plugs behind the case.
• Power lead: reserve a SATA or LP4 connector for the StarTech installation. Sonnet needs neither.
• Host access: keep the host’s boot storage and recovery keyboard on hardware that will stay with the host.

If your problem is simply a crowded mini PC with no PCIe slot, a powered USB hub is the appropriate expansion route. A hub adds downstream ports; it doesn’t add a PCIe host controller for the VM to own.

Assign the controller, then label its ports

Follow the official Proxmox PCI passthrough procedure for your installed release. Enable IOMMU in firmware and complete the documented host preparation, then use this short card-specific path:

1. Shut down the guest and save its working configuration.
2. Open the VM’s Hardware tab and add the intended PCI device by its recorded controller address. Preserve any existing GPU or other passthrough entries.
3. If you want multiple controllers in that VM, add their separate PCI addresses as separate entries. One card can expose several PCI devices.
4. Start the guest, install its appropriate USB-controller driver if required, then connect a simple peripheral to identify each owned socket.
5. Label the physical ports with the guest/controller mapping and save that map with the VM notes.

Proxmox’s All Functions option groups functions such as 03:00.0 and 03:00.1. It doesn’t collect every downstream controller on a multi-controller card. Select the controller addresses you actually inventoried.

For PCIe presentation, Proxmox requires a q35 machine type. Ordinary PCI passthrough also exists, so don’t convert an established VM’s firmware just to copy a GPU tutorial. Follow the guest’s supported configuration. If host binding needs attention, scope it to the intended PCI device; a blanket blacklist of the host USB driver can take your other USB ports with it.

Make the second start part of the test

A successful first launch is the beginning of the check. Before you put anything important on the card:

• Confirm the guest sees the expected controller and peripheral.
• Unplug and reconnect a suitable test device, using the guest’s eject procedure for storage.
• Shut down the guest normally, start it again, and repeat the device operation.
• Test a guest reboot and a planned host reboot, then confirm the port mapping still matches your notes.

If a device disappears, record which transition caused it and inspect the guest and host logs before changing settings. You want a repeatable routine, not a lucky first boot. Use disposable files for storage checks and keep the host recovery path available throughout.

Port power: enough for the peripheral, not a laptop charger

StarTech’s USB 3 rating works out as 5V × 0.9A = 4.5W per port. Sonnet’s is 5V × 1.5A = 7.5W per port. Those are maker supply limits, not what an idle dongle draws. Keep a peripheral’s own power adapter connected when its maker requires one, and use a suitable data cable for 10Gbps devices.

Choose PEXUSB3S44V for the four-controller layout and low-profile option. Choose the Sonnet for one guest’s four-port 10Gbps setup with no auxiliary PSU lead. If you only need to hand one USB device to a VM, try Proxmox’s existing device passthrough first. Buy the extra controller when it solves the ownership problem you actually have.