Thank you for your response.
I am sorry about the vague question.
Actually my NVR showing the alert correctly, when I unplug the HDD it shows 'No HDD' message.
I need to get all the events using an API. I see that it is possible by using the url...
Is it possible to detect the hard disk failure using the event manager. Can anyone share some idea about detecting hard disk not connected or not recording events?