[andrystepa]

Разобрался. В FAQ на сайте производителя вот что написано:
Q: I installed VirtualBox from my distributions repositories and I can't access my USB devices or see an option to enable USB.
A: You must install the PUEL Edition of VirtualBox. The OSE version does not include RDP, USB, iSCSI and SATA support. See the Wiki Editions page for an explanation of the differences between the two VB versions.

Q: I connect an USB device, but it isn't grabbed by the VM. What's going on?
A: Are you using the OSE version or the PUEL version? The OSE version does not provide USB functionality. If you use the PUEL version, read the Wiki and manual for how to set it up in Linux Hosts. Windows systems should work automatically. There will be a question for a driver on the Host once VB grabs it. Continue the installation, letting it search for a driver automatically. If you get a prompt about driver signatures, just Continue Anyway.

То есть существует две версии VirtualBox - OSE - Open Suorce Edition и PUEL - Personal Use and Evaluation License
Так вот Open Source не дает подключать USB диски. Надо качать PUEL версию.