_base_dir_file is base image data. a image hava a base image data in a compute node(_base) you set use_cow_images=true, each image have a base data mirroring and incremental data.
_base_dir_file is base image data. a image hava a base image data in a compute node(_base) images= true, each image have a base data mirroring and incremental data.
you set use_cow_