protected Void createVolumeAsyncCallback(
      AsyncCallbackDispatcher<? extends BaseImageStoreDriverImpl, DownloadAnswer> callback,
      CreateContext<CreateCmdResult> context) {
    DownloadAnswer answer = callback.getResult();
    DataObject obj = context.data;
    DataStore store = obj.getDataStore();

    VolumeDataStoreVO volStoreVO = _volumeStoreDao.findByStoreVolume(store.getId(), obj.getId());
    if (volStoreVO != null) {
      if (volStoreVO.getDownloadState() == VMTemplateStorageResourceAssoc.Status.DOWNLOADED) {
        if (s_logger.isDebugEnabled()) {
          s_logger.debug(
              "Volume is already in DOWNLOADED state, ignore further incoming DownloadAnswer");
        }
        return null;
      }
      VolumeDataStoreVO updateBuilder = _volumeStoreDao.createForUpdate();
      updateBuilder.setDownloadPercent(answer.getDownloadPct());
      updateBuilder.setDownloadState(answer.getDownloadStatus());
      updateBuilder.setLastUpdated(new Date());
      updateBuilder.setErrorString(answer.getErrorString());
      updateBuilder.setJobId(answer.getJobId());
      updateBuilder.setLocalDownloadPath(answer.getDownloadPath());
      updateBuilder.setInstallPath(answer.getInstallPath());
      updateBuilder.setSize(answer.getTemplateSize());
      updateBuilder.setPhysicalSize(answer.getTemplatePhySicalSize());
      _volumeStoreDao.update(volStoreVO.getId(), updateBuilder);
      // update size in volume table
      VolumeVO volUpdater = volumeDao.createForUpdate();
      volUpdater.setSize(answer.getTemplateSize());
      volumeDao.update(obj.getId(), volUpdater);
    }

    AsyncCompletionCallback<CreateCmdResult> caller = context.getParentCallback();

    if (answer.getDownloadStatus() == VMTemplateStorageResourceAssoc.Status.DOWNLOAD_ERROR
        || answer.getDownloadStatus() == VMTemplateStorageResourceAssoc.Status.ABANDONED
        || answer.getDownloadStatus() == VMTemplateStorageResourceAssoc.Status.UNKNOWN) {
      CreateCmdResult result = new CreateCmdResult(null, null);
      result.setSuccess(false);
      result.setResult(answer.getErrorString());
      caller.complete(result);
    } else if (answer.getDownloadStatus() == VMTemplateStorageResourceAssoc.Status.DOWNLOADED) {
      CreateCmdResult result = new CreateCmdResult(null, null);
      caller.complete(result);
    }
    return null;
  }
  @Override
  public void downloadVolumeToStorage(
      DataObject volume, AsyncCompletionCallback<DownloadAnswer> callback) {
    boolean downloadJobExists = false;
    VolumeDataStoreVO volumeHost = null;
    DataStore store = volume.getDataStore();
    VolumeInfo volInfo = (VolumeInfo) volume;
    RegisterVolumePayload payload = (RegisterVolumePayload) volInfo.getpayload();
    String url = payload.getUrl();
    String checkSum = payload.getChecksum();
    ImageFormat format = ImageFormat.valueOf(payload.getFormat());

    volumeHost = _volumeStoreDao.findByStoreVolume(store.getId(), volume.getId());
    if (volumeHost == null) {
      volumeHost =
          new VolumeDataStoreVO(
              store.getId(),
              volume.getId(),
              new Date(),
              0,
              Status.NOT_DOWNLOADED,
              null,
              null,
              "jobid0000",
              null,
              url,
              checkSum);
      _volumeStoreDao.persist(volumeHost);
    } else if ((volumeHost.getJobId() != null) && (volumeHost.getJobId().length() > 2)) {
      downloadJobExists = true;
    }

    Long maxVolumeSizeInBytes = getMaxVolumeSizeInBytes();
    if (volumeHost != null) {
      start();
      Volume vol = _volumeDao.findById(volume.getId());
      DownloadCommand dcmd =
          new DownloadCommand(
              (VolumeObjectTO) (volume.getTO()), maxVolumeSizeInBytes, checkSum, url, format);
      dcmd.setProxy(getHttpProxy());
      if (downloadJobExists) {
        dcmd = new DownloadProgressCommand(dcmd, volumeHost.getJobId(), RequestType.GET_OR_RESTART);
        dcmd.setResourceType(ResourceType.VOLUME);
      }

      EndPoint ep = _epSelector.select(volume);
      if (ep == null) {
        s_logger.warn("There is no secondary storage VM for image store " + store.getName());
        return;
      }
      DownloadListener dl = new DownloadListener(ep, store, volume, _timer, this, dcmd, callback);
      ComponentContext.inject(dl); // auto-wired those injected fields in DownloadListener

      if (downloadJobExists) {
        dl.setCurrState(volumeHost.getDownloadState());
      }

      try {
        ep.sendMessageAsync(dcmd, new UploadListener.Callback(ep.getId(), dl));
      } catch (Exception e) {
        s_logger.warn(
            "Unable to start /resume download of volume "
                + volume.getId()
                + " to "
                + store.getName(),
            e);
        dl.setDisconnected();
        dl.scheduleStatusCheck(RequestType.GET_OR_RESTART);
      }
    }
  }