int getOnDiskSizeWithHeader() {
      expectState(State.BLOCK_READY);
      return onDiskBlockBytesWithHeader.size() + onDiskChecksum.length;
    }
Returns the on-disk size of the block. Can only be called in the "block ready" state.
@return the on-disk size of the block ready to be written, including the header size, the
        data and the checksum data.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java