The NFS driver, and other drivers based off of it, work quite differently than a traditional block storage driver.
The NFS driver does not actually allow an instance to
access a storage device at the block level. Instead, files
are created on an NFS share and mapped to instances, which
emulates a block device. This works in a similar way to
QEMU, which stores instances in the
/var/lib/nova/instances
directory.
