@Override
  public ExtendedCell getFirstKeyCellInBlock(ByteBuff block) {
    int keyLength = block.getIntAfterPosition(Bytes.SIZEOF_INT);
    int pos = 3 * Bytes.SIZEOF_INT;
    ByteBuffer key = block.asSubByteBuffer(pos + keyLength).duplicate();
    return createFirstKeyCell(key, keyLength);
  }
Just copy data, do not do any kind of compression. Use for comparison and benchmarking.
hbase-common/src/main/java/org/apache/hadoop/hbase/io/encoding/CopyKeyDataBlockEncoder.java