private MStorageDescriptor convertToMStorageDescriptor(StorageDescriptor sd)
      throws MetaException {
    if (sd == null) {
      return null;
    }
    MColumnDescriptor mcd = createNewMColumnDescriptor(convertToMFieldSchemas(sd.getCols()));
    return convertToMStorageDescriptor(sd, mcd);
  }
Converts a storage descriptor to a db-backed storage descriptor.  Creates a
  new db-backed column descriptor object for this SD.
@param sd the storage descriptor to wrap in a db-backed object
@return the storage descriptor db-backed object
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java