[Openstack][cinder] scheduler filters

Hello All, I read that capacity filters for cinder is the default, so, if I understood well, a volume is placed on the backend where more space is available. Since my two backends are on storage with same features, I wonder if I must specify a default storage backend in cinder.conf or not. Must I create a cinder volume without cinder type and scheduler evaluate where there is more space available? Thanks Ignazio