private static int calcCompactionThreshold(int ct) {
    if (ct == DiskStoreFactory.DEFAULT_COMPACTION_THRESHOLD) {
      // allow the old sys prop for backwards compat.
      if (System
          .getProperty(GeodeGlossary.GEMFIRE_PREFIX + "OVERFLOW_ROLL_PERCENTAGE") != null) {
        ct = (int) (Double.parseDouble(System
            .getProperty(GeodeGlossary.GEMFIRE_PREFIX + "OVERFLOW_ROLL_PERCENTAGE", "0.50"))
            * 100.0);
      }
    }
    return ct;
  }
The unique id for this disk store.

Either set during recovery of an existing disk store when the IFREC_DISKSTORE_ID record is read
or when a new init file is created.
geode-core/src/main/java/org/apache/geode/internal/cache/DiskStoreImpl.java