code: func IsDir(root string) (bool, error) {
  	if osutil.DirExists(filepath.Join(root, "sha1")) {
  		return true, nil
  	}
  	if osutil.DirExists(filepath.Join(root, blob.RefFromString("").HashName())) {
  		return true, nil
  	}
  	return false, nil
  }
docs: // IsDir reports whether root is a localdisk (file-per-blob) storage directory.