'Retrieve stats info from volume group.'

def _update_volume_stats(self):

    data = {}
    backend_name = self.configuration.safe_get('volume_backend_name')
    data['volume_backend_name'] = (backend_name or self.volume_backend_name)
    data['vendor_name'] = 'Open    Source'
    data['driver_version'] = self.get_version()
    data['storage_protocol'] = self.driver_volume_type
    self._ensure_shares_mounted()
    global_capacity = 0
    global_free = 0
    for share in self._mounted_shares:
        (capacity, free, used) = self._get_capacity_info(share)
        global_capacity += capacity
        global_free += free
    data['total_capacity_gb'] = (global_capacity / float(units.Gi))
    data['free_capacity_gb'] = (global_free / float(units.Gi))
    data['reserved_percentage'] = self.configuration.reserved_percentage
    data['QoS_support'] = False
    self._stats = data
