PI Tags showing values as Not connected and Com Fail respectively
Not sure what your question is, but I will assume you have a series of pi tags that read the stated values for a defined time range. I am further assuming the tags were updating normally, then began showing these error values, and then returned to updating normally.
Based on the values you communicated there appears to have been a break in the connection between the PI interface and the PI Data Archive. The potential causes are too numerous to list, but I would start looking at the event queue for that specified time range for some clues. I suspect there was a network change (firewall update, network device fail over, disconnected cable, etc.).
The second part of your question is not stated. I also assume you want good data backfilled to these pi points. If that is the case there are other posts about methods to backfill. My personal favorite is PowerShell. This resource may prove helpful: AddPIValue Properties
Yes James you are correct. I just needed best approach for the same.
What will be the best way to investigate it.
These are my suggestions based on my very limited knowledge of your situation. I would open the 'Event Viewer' on the PI Data Archive server and examine the logs for the time range in question. I included a screenshot with steps to view them for the time range. If that does not yield any clues I would then repeat that on the PI Interface server. I would search the PI Message Logs in PI System Management Tools. I would also consult with any network administrators in your organization to see if they performed any changes, or fixed any problems during that time. There is always the possibility your SCADA system had a communication failure with instruments measuring the device or system in question. Your SCADA engineers might be able to answer that question.
I believe those steps will reveal something to investigate further.
Retrieving data ...