Can't attach Secondary disk with IO options

[0xmeti]

Hello,
I created some images of type datablock.
Now, I want to attach them to a virtual machine via a disk block,

disk {
    image_id = opennebula_image.example.id
    size     = 10000
    target   = "vda"
    driver   = "qcow2"
  }

but there is no option for IO settings (like the ones available in the UI) in the disk parameters.
I want to configure the Throttling parameters and change the values for total, read, and write.

The only usable parameter for disk related to IO is policay which doesn't work for me.

io - (Optional) Set IO policy. Values are threads, native.