Hardware and performance

> 1. Concurrent access: I know that the maximum number of concurrent users (which still gives users an 'acceptable' response time) will vary depending on the type of user activity at that point in time. Will the stated configuration support 1500 concurrent users accessing the same quiz (without grinding the server to a halt)? If not, what's a more accurate figure? On our current LMS, large quizzes are staggered during the day, so there may actually be just 300 users at a time taking the quiz.

Just to make sure: We are talking about the capacity of the server (or servers) alone and assume that the network can deliver!

You are right. The server load depends very much on the type of activity being used. IMHO Chat is the worst then comes Quiz. So your "1500 concurrent users accessing the same quiz" sounds too optimistic for me. If your real figure is 300, that has a much better chance. Either way a PHP accelarator will be a _big_ boost.

> 2. With respect to using two servers, are there any components which should be beefed up (e.g. use more RAM on the Moodle (Apache) server; use a faster processor on the database server...)? Also, am I missing any essential components? I wish we could simply say 'buy the biggest we can afford', but everything needs to be justified.

RAM is clearly the most effective investment for better performance. Since you are talking about going beyond 2 GB make sure that your hardware and the operating system support that much. Also simply "having" more RAM is no guratee, you have to assign them work, like caching whole pages or querries!

There are lot of pointers in this forum. You seem to have gone through it, therefore I'm not citing them here.

> 3. O/S: We were planning to go Linux. However, a couple posts suggest "go Windows until you have proficient Linux support staff". For now, just one or two have dabbled in Linux. I'm now learning it myself. Is it too ambitious to assume that I'll be well versed in Linux by August? Should we go Windows for a while? If Windows, should any server components be beefed up or changed to support our requirements?

Building up a productive system for 14'000 users is a respectable job, whatever operating system you choose. The usual advice you get here is _not_ "go Windows until you have Linux support", rather "Windows is OK for evaluating Moodle, trial installations, etc. but Unix for more demanding environments".

With 14'000 users you belong to the latter! IMHO it is naiv to believe "one or two Linux dabblers" will stand the test.

The strategy "go Windows until you have Linux support" doesn't convice me either. From which direction do you expect Linux support? I know at least one institution which has planned a server for a similar size, started on Windows and now hitting the performance ceiling already with 5000 users! The inevitalble migration has started. The total effort of the administrators and the suffering of the users, I don't see any justification for that.

Talking about "migrating" courses: Also consider a phased out transition of courses (and users). The way the hardware keep on improving and the way software demands follow, you might want to start with a less demanding server infrastructure and plan it so that you can add/upgrade later.

Some thoughts... some experience, some mere prejudice

Firstly until you have actually run Moodle for some time you just don't know what you are going to need. You won't know the usage patterns or what activities will be used and when etc etc. So, the main thing is to leave your options open for expansion - don't buy anything too expensive and consider the possibility that you might have to buy a bigger machine at some point or even better split your Moodle installation. If you have more than one Moodle site then you can run them on different machines.

I personnally would NOT run MySql and Moodle on seperate machines. Firstly because it becomes much simpler to secure (just turn off networking in MySql) and it will be much more efficient as you don't have all that network latency to worry about.

To answer your questions...

1. 1500 concurrent access - are you sure? We have 16,000 registered users and the most we have ever seen logged on 'concurrently' is around the 80 mark, the average being much lower.

2. Buy the biggest you can afford I'm sure that you don't need me to tell you that lots of RAM and disk I/O make the biggest differences. Spend your money on fast disks and good RAID cards.

3. Don't go Windows. Setting up Moodle on Linux is a breeze with the sort of knowledge you can get in an afternoon. I get depressed when I think about installing Moodle on Windows - it is *much* trickier. People will argue about which distro to use for ever but my $00.02 would be to consider SuSE. Why? The installation and administration tools are excellent and will keep you away from the tricky command line and configuration file stuff for quite a long time.

EDIT:
Reading your post again, if your concurrent usage really is that high you *may* want to consider looking at Postgres as your database. It is much more tunable for high volumes than MySql (see http://docs.moodle.org/en/Arguments_in_favour_of_PostgreSQL for more information). The downside is that it requires rather more administration skill and is not quite as well supported (ie, you will probably be living on Moodle version behind).