func (s *Storage) NewReader(ctx context.Context, dataRefs []*DataRef) io.ReadCloser {
	if len(dataRefs) == 0 {
		return ioutil.NopCloser(&bytes.Buffer{})
	}
	return newReader(ctx, s.objC, s.prefix, dataRefs)
}
func (s *Storage) NewReader(ctx context.Context, dataRefs []*DataRef) io.ReadCloser {
	if len(dataRefs) == 0 {
		return ioutil.NopCloser(&bytes.Buffer{})
	}
	return newReader(ctx, s.objC, s.prefix, dataRefs)
}
// NewReader creates an io.ReadCloser for a chunk.
// (bryce) The whole chunk is in-memory right now. Could be a problem with
// concurrency, particularly the merge process.
// May want to handle concurrency here (pass in multiple data refs)