qemu-img create -f raw /var/lib/vz/images/usb.img 8G
drive_add 0 file=/var/lib/vz/images/usb.img,if=none,id=drive-usb0,format=raw,cache=none
device_add usb-storage,id=drive-usb0,drive=drive-usb0,removable=on
device_del drive-usb0
Możesz nawet bootować z takiego pendrive, a nawet dodać to na stałe do maszyny:
qm set <VMID> -args "-drive file=/var/lib/vz/images/usb.img,if=none,id=drive-usb0,format=raw,cache=none -device usb-storage,id=drive-usb0,drive=drive-usb0,removable=on"