All,
Thanks for the input so far. Just to be clear, I'm certainly not worried about running out of space to store the WeatherCatData folder. My query (though I realise I wasn't precise) was around performance and whether a database can just continue to grow without being unwieldy or slowing a system down - in the same way large spreadsheets with millions of rows can take forever to open.
With regard to my ageing hard drive and it's imminent doom: let it fail is my attitude. It's only there to run WeatherCat. So long as my data is backed up daily (which it is through writing the 20:00 backup file into the the cloud each day, and copying the 2 occurrences of it on the system drive via Time Machine) then it doesn't matter if my mac drive fails, does it?
Let me explain my thinking:
To replace my hard drive now means I'll have to power down my system, faff with installing a new one, then spend an afternoon installing the OS, plus WeatherCat, drivers etc. All this time I'm relying on the Davis's data logger to store the data which will eventually be incorporated into the database, once retrieved and the logger downloaded.
That is a significant disruption.
So, instead I'll leave the aged mac to soldier on and keep backing up as usual. When I come home from work one day and find it's died, I'll have to carry out the process above anyway... only I won't need to manually power down the system at least!
In reality, I have two macs. The elder of the two runs WeatherCat. When it dies, I'll simply repurpose my current "daily use" mac to run WeatherCat and buy a new one to replace my daily mac. At nearly 10 years old, this one owes me nothing.
When all's said and done, the Davis logs for 2 weeks without any input from me or a Mac. That's plenty of time to replace either a hard drive, or a whole computer.
Just so long as my backup is safe!
There you go... not quite the orthodox "belt and braces" approach most folks take as contingency, but this mac only runs WeatherCat, there is no other data on this system I care to keep, no photos, emails, music etc. All that is done by my newer mac. This one simply sits in the corner of a quiet room and plods on stoically with it's weather data farming.
Hope you don't all think I'm too insane.