@Override protected synchronized void read(long offset,byte[] b) throws IOException {
  if (byteBuffer != null) {
    byteBuffer.position((int)offset);
    byteBuffer.get(b);
  }
 else {
    throw new IOException("Read failed, file " + getPath() + " not mapped for I/O");
  }
}

@ Override protected synchronized void read ( long offset , byte [ ] b ) throws IOException { if ( byteBuffer != null ) { byteBuffer . position ( ( int ) offset ) ; byteBuffer . get ( b ) ; } else { throw new IOException ( "Read failed, file " + getPath ( ) + " not mapped for I/O" ) ; } }
reads a number of bytes from the rrd file on the disk
