code: func (c *sioClient) IID() (string, error) {
  	if err := c.init(); err != nil {
  		return "", err
  	}
  
  	// if instanceID not set, retrieve it
  	if c.instanceID == "" {
  		guid, err := c.getGUID()
  		if err != nil {
  			return "", err
  		}
  		sdc, err := c.sysClient.FindSdc("SdcGUID", guid)
  		if err != nil {
  			klog.Error(log("failed to retrieve sdc info %s", err))
  			return "", err
  		}
  		c.instanceID = sdc.Sdc.ID
  		klog.V(4).Info(log("retrieved instanceID %s", c.instanceID))
  	}
  	return c.instanceID, nil
  }
docs: // IID returns the scaleio instance id for node