private void writeIFRecord(byte b, long v) {
    assert lock.isHeldByCurrentThread();
    try {
      ByteBuffer bb = getIFWriteBuffer(OPLOG_FILE_ID_REC_SIZE);
      bb.put(b);
      bb.putLong(v);
      bb.put(END_OF_RECORD_ID);
      writeIFRecord(bb, false); // don't do stats for these small records
    } catch (IOException ex) {
      DiskAccessException dae = new DiskAccessException(
          String.format("Failed writing data to initialization file because: %s", ex),
          parent);
      if (!compactInProgress) {
        parent.handleDiskAccessException(dae);
      }
      throw dae;
    }
  }
Maximum number of bytes used to encode a DiskRegion id.
geode-core/src/main/java/org/apache/geode/internal/cache/DiskInitFile.java