could you all please help me with my questions?
What is "$CFG->tempdir" used for and why should it be shared among cluster nodes?
Would it be possible to use fast local directories for "$CFG->tempdir" when sessions are sticky?
Things that can safely be stored on each separate server use a localcachedir. This defaults to something inside moodledata (== shared) but in your situation you should set it. This is documented in config-dist.php: https://github.com/moodle/moodle/blob/master/config-dist.php#L430
I had to swap out my moodledata directory in order to have enough storage space available.
Therefore I also used "localcachdir" for the necessary performance and pointed to an area of the local disk. Unfortunately the directory seems to grow more and more. At the moment it is already about 300GB. It seems to me that the cache is not being cleaned up. What can I do about it?