Device lock by virtual machine

Hi,

I'm using proxmox VE 3.1 and I'm having a problem with my backup device.
The device is an RD1000, each cartdrige is recognize as a hard drive.

So I've add sata1: /dev/sdb, media=disk,backup=no on my <VMID>.conf
Unfortunately, when I want to eject the cartdridge, the virtual machine have lock it and the only way to eject it, is to shutdown the virtual machine (the device isn't mounted on the virtual machine).

So I'm looking for a way, to only lock the device when the virtual machine mount the device (and not lock it at boot as it does now).

Best regards,