core/src/main/java/com/orientechnologies/orient/core/storage/cache/local/twoq/O2QCache.java
@Override
  public final void closeStorage(final OWriteCache writeCache) throws IOException {
    if (writeCache == null) {
      return;
    }

    cacheLock.acquireWriteLock();
    try {
      final long[] filesToClear = writeCache.close();
      clearFiles(writeCache, filesToClear);
    } finally {
      cacheLock.releaseWriteLock();
    }
  }
@Override
  public final void closeStorage(final OWriteCache writeCache) throws IOException {
    if (writeCache == null) {
      return;
    }

    cacheLock.acquireWriteLock();
    try {
      final long[] filesToClear = writeCache.close();
      clearFiles(writeCache, filesToClear);
    } finally {
      cacheLock.releaseWriteLock();
    }
  }
Performs following steps:
<ol>
<li>If flag {@link OGlobalConfiguration#STORAGE_KEEP_DISK_CACHE_STATE} is set to <code>true</code> saves state of all queues of
2Q cache into file {@link #CACHE_STATE_FILE}.The only exception is pinned pages they need to pinned again.</li>
<li>Closes all files and flushes all data associated to them.</li>
</ol>

@param writeCache Write cache all files of which should be closed. In terms of cache write cache = storage.