static long numBytes(long datasize, int bytesPerChecksum) {
    return numChunks(datasize, bytesPerChecksum) * HFileBlock.CHECKSUM_SIZE;
  }
Returns the number of bytes needed to store the checksums for a specified data size
@param datasize         number of bytes of data
@param bytesPerChecksum number of bytes in a checksum chunk
@return The number of bytes needed to store the checksum values
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/ChecksumUtil.java