docs: def _get_existing_logical_drives(raid_adapter):
      """Collect existing logical drives on the server.
  
      :param raid_adapter: raid adapter info
      :returns: existing_logical_drives: get logical drive on server
      """
      existing_logical_drives = []
      logical_drives = raid_adapter['Server']['HWConfigurationIrmc'][
          'Adapters']['RAIDAdapter'][0].get('LogicalDrives')
      if logical_drives is not None:
          for drive in logical_drives['LogicalDrive']:
              existing_logical_drives.append(drive['@Number'])
  
      return existing_logical_drives