private static String getStoreIdForDirName(String storeDirName) {
    return storeDirName.startsWith(STORE_DIR_PREFIX) ? storeDirName.substring(STORE_DIR_PREFIX.length()) : null;
  }
Parse store id from a possible store reserve directory name.
@param storeDirName the name of a possible store reserve directory
@return the parsed store id, or {@code null} if the directory name did not start with the correct prefix.
ambry-store/src/main/java/com/github/ambry/store/DiskSpaceAllocator.java