@Test
  public void testDelayedDiskIdCreationInOverflowOnlyMode() {
    diskProps.setPersistBackup(true);
    diskProps.setRolling(false);
    diskProps.setMaxOplogSize(1024 * 1024);
    diskProps.setSynchronous(false);
    diskProps.setOverflow(true);
    diskProps.setBytesThreshold(10000);
    diskProps.setTimeInterval(0);
    diskProps.setOverFlowCapacity(1);
    region = DiskRegionHelperFactory.getAsyncOverFlowOnlyRegion(cache, diskProps);
    final byte[] val = new byte[1000];
    region.put("1", val);
    DiskEntry entry = (DiskEntry) ((LocalRegion) region).basicGetEntry("1");
    assertTrue(entry instanceof AbstractDiskLRURegionEntry);
    assertNull(entry.getDiskId());
    region.put("2", val);
    assertNotNull(entry.getDiskId());
    entry = (DiskEntry) ((LocalRegion) region).basicGetEntry("2");
    assertTrue(entry instanceof AbstractDiskLRURegionEntry);
    assertNull(entry.getDiskId());
  }
Tests delayed creation of DiskID in overflow only mode
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/OplogJUnitTest.java