void addDiskRegion(DiskRegion dr) {
    if (dr.isBackup()) {
      PersistentOplogSet oplogSet = getPersistentOplogSet(dr);
      if (!isOffline()) {
        oplogSet.initChild();
      }

      DiskRegion old = drMap.putIfAbsent(dr.getId(), dr);
      if (old != null) {
        throw new IllegalStateException(
            "DiskRegion already exists with id " + dr.getId() + " and name " + old.getName());
      }
      getDiskInitFile().createRegion(dr);
    } else {
      overflowMap.add(dr);
    }
    if (getOwnedByRegion()) {
      ownCount.incrementAndGet();
    }
  }
Returns a set of the disk regions that are using this disk store. Note that this set is read
only and live (its contents may change if the regions using this disk store changes).
geode-core/src/main/java/org/apache/geode/internal/cache/DiskStoreImpl.java