Hi Danilo,
The reason why you see duration value 3600 instead of 180 is most likely because remote monitoring server is configured to close logs every 60 minutes. You can check that by going to Home -> Monitoring And Alerting -> Monitor -> Settings -> Remote Monitoring Server Settings, 'Data Collection' tab, 'Close logs every X Minutes' setting.
Remote Monitoring Server polls ping metric accoring to the configured polling interval (180 seconds), but if the value has not changed since last time, the metric value is not logged. This is done to minimize size of the logs that need to be stored. After the logs are closed, they are uploaded to server for processing. Eventually server processes the logs and stores the values in the database. The processing of logs is done on per log basis, so if the ping metric does not change its value for 60 minutes there's going to be a single entry for this metric in the log and as a result this value will be stored with appropriate duration (3600 in your case).
With this said, it's important to note that data in vMonitorAllMetricData is not a simple log of metric polling results - it's pre-processed data that is organized for the purposes of reporting historical data in historical performance viewer. Specifically the Duration field bsically specifies how long the metric's value remained unchainged since the time specified in Timestamp field.
I'm not quite clear on what exactly you are asking in your other question. Could you please give me an example of your situation - this should help me better understand your question and hopefully answer it.
Best regards,
Vadim