int getUncompressedSizeWithoutHeader() {
      expectState(State.BLOCK_READY);
      return baosInMemory.size() - HConstants.HFILEBLOCK_HEADER_SIZE;
    }
The uncompressed size of the block data. Does not include header size.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java