Save data for 1 week

Hello all, I have a small project and need to save data for one week in offline mode. I can save data through Blynk in online mode, but for offline mode, I need to save data in the ESP32’s memory along with their date and time. Can I make it and if yes, how can I achieve it?

You should use LittleFS

How you do it, how you then write this saved data to Blynk when it’s online again (if that’s what you want), how you clear the data when you’ve done, how you switch over to storing data to LittleFS when the device is offline etc etc will depend very much on your project.
Your LittleFS file system will depend on how many datastreams you’re using, and you’ll need to give some careful thought to the data sampling rate, so you don’t store silly amounts of data.

You will need to use Blynk.config and Blynk.connect rather than Blynk.begin, and manage your own internet connection, so your device runs offline.

I’d success that you take a look at LittleFS (it’s almost identical to SPIFFS, and there are lots of SPIFFS tutorials around) and start experimenting.