In the last several years my university ran several very successful small-scale (1000 or so users, up to 50 simultaneous active users) Moodle deployments. Each was based on single server and ran at departmental level. They all worked on Linux/Apache/MySQL. It was policy of the university to not engage in administering Moodle installations so I ended as administrator of one of them, even though I am not professional administrator or PHP developer.
Now the whole university plans to integrate all the projects into one "big" university-level Moodle installation, but due reasons, which are related to financing, manpower and already procured servers. they want it on Windows/IIS/MS SQL. Such installation would have up to 500 simultaneous active users in peak moments from up to 15000 or so active accounts. We would add up to 4000 accounts each year for our new students and remove the roughly same number of accounts for our graduates. Of course we are prepared to use load balancing, several web servers and MS SQL clustering to achieve performance.
In my capacity of "successful" Moodle administrator I was asked a question I cannot answer, based on my experience - are there any known problems with using Moodle in such scale in such environment?
I've already read in the docs that PHP is basically 32-bit app under Windows, so tables are limited to 2 billion records in table. I am making steps to get input from the other Moodle admins at the university to try and judge how big will the tables become (my own departments Moodle database is not quite representative for the activity of an average user).
So I would appreciate input and opinions from people with similar deployments regarding this and other potential problems.
Thanks is advance!