question: @ 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" ) ; } }
target:  Reads a number of bytes from the RRD file on the disk