Hi @vege44 I had a quick look at this.
If you edit /share/CACHEDEV1_DATA/.system/idbserver.conf (depending on your actual volume name), then find the myidbserver config block, then change the value of ENABLE to false, this then shows in the MMC web UI as thumbnail generation disabled (it’s not a live change, so reload the MMC UI).
Note: this key-value pair is most-likely changed after the thumbnail service has been enabled/disabled so it’s doubtful it will actually stop any thumbnails being generated. It won’t trigger the daemon that generates thumbnails to behave any differently in your current QTS session, but would most likely apply when the service is next restarted.
However, I hope this has at-least been some help. It seems the thumbnail generator is called ‘idbserver’, so that’s probably what you’d need to look-for in the way of processes or configs. That’s where I’d concentrate my efforts. 