long generateRegionId() {
    long result;
    do {
      result = regionIdCtr.getAndIncrement();
    } while (result <= MAX_RESERVED_DRID && result >= MIN_RESERVED_DRID);
    return result;
  }
Called when creating a new disk region (not a recovered one).
geode-core/src/main/java/org/apache/geode/internal/cache/DiskStoreImpl.java