Thanks to all for the replies. Unfortunately none is really relevant to my issue. My library has been large for years and even though I am adding to it on a daily basis it has been only for some months that it shows problems (above 200 k tracks maybe). Media Center in this regard was much better than iTunes or Audirvana but apparently now I have reached the ceiling.
No, you're wrong. MC has been tested with libraries with over 1,000,000 tracks. It gets a little slower at that level. Even at 200k it should be a little slower than say 10k. But it should not influence CPU usage.
Try running activity monitor and sort by CPU usage and see what is using CPU. If it's MC, see how *much* CPU it's using.
Funny when I clicked to get system informations it never opens: it is working and working but it never comes.
Something is broken. The system information window should show up just about instantly. Since it isn't showing up, something is wrong. I'm assuming you've tried restarting MC and rebooting the mac?
But fan stopped so it is one less noise. Obviously there are many informations to pick up with my large library. I am afraid Drobo will explode at some stage with the hard drives running full speed for this information check.
No. System Info doesn't scan all of the tracks in your library. It should not cause any disk activity at all. System Info is just a screen that shows you statistics about your library and system, plus information on what background processes are running. It won't cause disk access.
Regarding The mbp is 2011 but on Apple website they say that only 15 and 17" are concerned, mine is a 13".
Ok, so yours probably has an i5 instead of an i7. It should still be fast enough to run MC with a medium-large library. You might try running the MC benchmark just to see what score it gets for reference: Help > Benchmark > Run benchmark . I'm guessing yours will score in the 1800 - 2000 range. But your MC doesn't seem to be acting correctly, so maybe not. You might need to reinstall MC. It's non-destructive and pretty quick, so it's not a bad idea to try.
There's also the possibility that you have a hardware issue of some sort: Failing drive, failing CPU, or maybe bad RAM. It wouldn't be all that unusual on a 5+ year old machine. I hope your machine is just fine, but it's possible it has an issue.
Good luck and let us know what you find.
Brian.