int getOnDiskSizeWithoutHeader() {
      expectState(State.BLOCK_READY);
      return onDiskBlockBytesWithHeader.size() + onDiskChecksum.length
        - HConstants.HFILEBLOCK_HEADER_SIZE;
    }
Returns the on-disk size of the data portion of the block. This is the compressed size if
compression is enabled. Can only be called in the "block ready" state. Header is not
compressed, and its size is not included in the return value.
@return the on-disk size of the block, not including the header.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java