I already spoke to another who said Apache/Moodle PHP on one linux box running Zend and MySql on a few other Linux boxes replicated can easily support 20,000 Users.
1. Is this the right forum for this question?
2. Has this question already been thrashed out?
3. Are there examples of enterprise level installations like I am wanting to know about. Can Moodle scale up to 40,000? 100,000 users?
4. Is this the wrong question?
3. Please see Installations_10000_plus and Installations_30000_plus. Not all of those sites employ developers. The Open University (UK) (about 450,000 users) does employ a lot of developers, but mostly to add new features and integrate Moodle with our other systems, for for performance reasons.)
This site (also about 450,000 users, fairly heavy forum use, but otherwise not typical) only just moved from a single server to separate DB and web server set up.
In any large and complex bits of software, there will be performance bottlenecks. Eventually one of them gets bad enough that it actually starts being a problem for someone, so it becomes a focus for attention and gets fixed. Over time this leads to software that performs very well. There have been enough large Moodle installations in existence for long enough that this process has happened. The open source nature of Moodle, which means that people collaborate, helps here. If you look at the coding guidelines, you will see that performance is discussed there. The basic techniques to avoid the obvious problems are known.
You may also want to look at Top 10 Moodle Myths and Documents useful for decision makers.
1 & 2. It is and it's been mostly covered through various threads.
3. Yes, you can look through the installation statistics. http://moodle.org/stats/
4. Just like "How many concurrent users can x handle?" the question is ambiguous. Moodle allows you to do quite a lot, and to get valid and accurate answers, you need to be more specific. If you're moodle.org and most of your traffic is coming from the forum module and downloads, you could easily handle hundreds if not thousands of 'concurrent' users. However, if you're hitting Moodle's /my to get your entire course list and everyone has hundreds of courses, then go on a vacation since that wont finish. In my tests, the forum, wiki, and calendar modules were the fastest.
I don't know how Blackboard works, but I'm sure it is no more 'enterprise ready' than Moodle. To get anything to scale past a certain point, you'll need to throw money at it. The nice thing about Moodle is that it is open source and if you are a large organization, then you may already have the staff that is able to do it.
If the admin you were talking to about Moodle tested Moodle with 11,000 users hitting all of the pages, then he did it wrong. Very, very, very few installations of any LMS actually has that sort of load and when they do, I would think they have a user base that measures in the hundreds of thousands. I doubt even Blackboard/Vista/WebCT are capable of scaling to those levels out of the box with no hardware investment. (but I may be wrong since I don't know anything about those products)
From first-hand experience, I can tell you that Moodle is capable of scaling to past 60,000, 3,500 courses and all on one (powerful) server using only the internal cache. There were a few performance related stumbling blocks uncovered along the way, but those were one-liner fixes that required a bit of work in uncovering. (db sessions - BINARY type casts prevented MySQL from using keys, get_my_courses() - we (ab)used it, it was really slow but was optimized, etc)
Those are two examples since I could only remember two. If there were a ton of optimizations required, I would be able to provide more examples but since there weren't, you have only two examples. Was that philosophical enough to somewhat disprove admin argument #1?
And as for modules, I would think the cost would come from rewriting bad modules or writing new ones. If it was badly written, don't use it. If you need new functionality, would the company behind another LMS do it for you for free? I don't think so.
That's not to say that there isn't some planning involved at that sort of scale. We have quite a lot of hardware but noting a capable sysadmin couldn't handle.
Admin you talked with is a bit misinformed, or tried to run Moodle on an under-powered system or without adequate help. Scaling Moodle or any LMS to support a significant number of users requires some planning on the hardware, OS and DB side. Moodle handles scaling as well as any other system when the homework is done. There are a number of organizations with 22k users on Moodle, and some with over 100k users. There are some with even higher numbers that have customized Moodle, but not because it was necessary to do that. They just wanted Moodle to behave differently and that's one of the great things about open source software. You can have it your way!
When an organization deploys Moodle (or any LMS) as their chosen system, and they intend to support many thousands of users in a mission critical environment, one thing that cannot be overlooked is the support that will be required. It is naive of an organization that would be supporting say 22k users to think they could simply hand this over to the IT department as one of the many things they have to support, without hiring full time LMS administrators. Typically an organziation supporting 22k students, many hundreds of teachers and possibly thousands of courses is going to need to staff up with 6-10 full time people if this is mission critical. This would would include people handling authentication issues, backup, routine Moodle maintenance, teacher training and help desk and instructional design services to name a few.