public int read(long offset, ByteBuff dst) {
    return internalTransfer(offset, dst, READER);
  }
Transfers bytes from this buffers array into the given destination {@link ByteBuff}
@param offset start position in this big logical array.
@param dst    the destination ByteBuff. Notice that its position will be advanced.
@return number of bytes read
hbase-common/src/main/java/org/apache/hadoop/hbase/util/ByteBufferArray.java