boolean areAllStoresDown() {
    rwLock.readLock().lock();
    boolean storesAllDown = true;
    try {
      for (BlobStore store : stores.values()) {
        if (store.isInitialized()) {
          storesAllDown = false;
          break;
        }
      }
    } finally {
      rwLock.readLock().unlock();
    }
    return storesAllDown;
  }
Check if all stores on this disk are down.
@return {@code true} if all stores are down. {@code false} at least one store is up.
ambry-store/src/main/java/com/github/ambry/store/DiskManager.java