Relation between USB mass storage and physical drive

Hello
anyone in this list know how to make the relation between mass storage
device (USB)
and physical drive.
I get information about when i plug in USB mass storage device with
registerdevicenotification
the mass storage has no partition on it, i need to know what physical drive
the classpnp.sys creates, \PhysicaldriveX
What api can i use to make the relation between USB mass storage and
physical drive
in user mode ?
Thanks