code: public BlockMeta getBlockMeta(long blockId) throws BlockDoesNotExistException {
      for (StorageTier tier : mTiers) {
        for (StorageDir dir : tier.getStorageDirs()) {
          if (dir.hasBlockMeta(blockId)) {
            return dir.getBlockMeta(blockId);
          }
        }
      }
      throw new BlockDoesNotExistException(ExceptionMessage.BLOCK_META_NOT_FOUND, blockId);
    }
docs: Gets the metadata of a block given its block id.
  
  @param blockId the block id
  @return metadata of the block
  @throws BlockDoesNotExistException if no BlockMeta for this block id is found