Volume Mount/Dismount

i want to access the file data directly from the disk instead of geting it
from the disk File system. This involves me bypassing the local file system
and communicating to the disk directly. I have set up an IRP with the
appropriate parameters. Now upon calling IoCallDriver() for the Disk
object, it returns a status of STATUS_VOLUME_DISMOUNTED…
How does the volume come into the picture even when the FS is bypassed ?

TIA
RB.