We are in the middle of evaluating Moodle to be used in a University setting with up to 50,000 registered students in a variety of courses and anticipating several thousand simultaneous connections.
What we are hoping for here is to create a list of metrics that other Moodle sites have found to be meaningful in understanding what things are affecting the performance of Moodle at their sites. Some things might be obvious such as memory use or disk I/Os. Some may at first seem important, but you might have discovered them to be less significant.
We are not looking so much for a list of favorite tools to extract those metrics, though that could also be helpful, but a list of things to observe, especially to help anticipate possible problems.
Anyway, any observations you can contribute to such a list will be helpful. I will try to keep a tally and summary of comments and put it up either here or somewhere easily accessible.
Thank you for any information you can give.