Anyway, I have done some hours more of testing. The results are kind of surprising. The short answer is: Volumio seems to work with large amount of files.
The key to “happiness” was to disable the automatic database-update on each “BOOT”.
- using a “clean” new installtion with “no” music-storage attached
- /etc/mpd.conf (parameter auto_update should be set to No)
- config.json file under /volumio/app/plugins/music_service/mpd. Parameter auto_update must be set to “false”
- attach “large” music-storage
- using “ssh” and issuing “mpc --wait update” ==> takes about 2-3 hours until prompt returns
- works decently fine
From thereafter giving the Pi4 about 3-4 minutes of time after each “boot” and all further database updates triggered via “ssh”.
My explanation: the Pi4 needs a large amount of time after each reboot to update its database (unless update is disabled) and in this period of time it is extremly slow in “any reaction” to command. Probably one or another “boot” while the Pi4 was still updating its database (no “turning” on DB was visible in GUI) causes “strange” things concerning the database.
I will investigate further and maybe my experienced can help others.
To all of you: Have nice days and enjoy listening to music!