'Return size of volume to be managed by manage_existing.'

def manage_existing_get_size(self, volume, existing_ref):

    vdisk = self._manage_input_check(existing_ref)
    if self._get_vdiskhost_mappings(vdisk['name']):
        reason = _('The    specified    vdisk    is    mapped    to    a    host.')
        raise exception.ManageExistingInvalidReference(existing_ref=existing_ref, reason=reason)
    return (int(vdisk['capacity']) / units.Gi)
