openstack flavors contains only ephemeral disk (non-persistent storage and OS partitioned disk)

where cinder as its external storage, its can be linked with flavors.

I believe its taking from nova, where nova talks to internal storage and takes the disk space for OS image.

Do don't want to specify anything in nova.conf !!!!!

If u want to use the SAN for your Openstack environment, use the multiback driver and do the respective changes in the cinder.conf

http://docs.openstack.org/trunk/openstack-block-storage/admin/content/multi_backend.html (http://docs.openstack.org/trunk/opens...)

And can we say that the ephemeral disk used to store root file system of the VM OS? Yes, its for root FS.. You can ensure by creating the instance with different flavor types.