Mounting Pi Zero as USB gadget for Heat pump data logging

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We’re are trying to monitor air exhaust heat pumps without purchasing the costly proprietary uplink kit and subscription. You can setup the logging function to record all data every 5 seconds to an attached USB stick, but we want this data in emoncms in as near to real time as possible.

So far I’ve setup a Raspi Zero in OTG mode to appear as a Mass Storage device and added an external ethernet port on the SPI pins, so that I can ssh into the pi.

While I can save data on the mass storage side, I’m not sure what the best way of accessing that data on the pi-side is, so that I can process it and forward it on. Others using OTG gadgets seem to switch between the two by unmounting and mounting with a cron job, but I’m not sure how the heat pump would handle this.

I’ve tried copying the mounted image file and then mounting the copy and it seems to work, but concerned about data integrity. Anyone with experience or thoughts, is there a non-intrusive way to look at the data while maintaining its integrity?