Hi Marvin,
We've been running an LTSP server on a Xeon system quite similar to yours but with 2 GB RAM. There are 25 terminals connected at the moment, but not all of them are in use at the same time.
Yesterday was the first time I saw 20 users logged in concurrently. No problem so far.
We are running KDE and all those things you mentioned except Evolution. But we have tested WINE and that is a real stress for the CPUs: with 15 users working on Word it's almost constantly eating 60 - 70 % CPU power (though it spreads to 4 CPUs, so you don't feel it when working with the system).
Actually, it's easy to upgrade the RAM of the server but I admit that it's very difficult to upgrade the network/physical connections. Eventhough the IBM xSeries 345 server has a gigabit ethernet, still it can only use of up to 100Mbps because the existing NICs on the workstations and switches are all in 10/100Mbps.
Part of the clients had 10 Mbps cards which slowed them down and caused a lot of connection chaos - I changed everything in the network to 100 Mbps, now the system runs really stable.
Well, this is on the application side issue. Maybe we can just double the RAM to 8GB for the server if that would be the case.
I don't know... As I mentioned, we use the server with 2 GB Ram for up to 25 clients. Now I have monitored the system for the past weeks with ksysguard. You can see that Linux will take as much RAM as needed first, the RAM in use being almost filled up to 2 GB for about 10 users. Then only the use of it changes, i. e. system, cache etc. with every new client logging in. When someone logs out, memory is given free, the same happens when heavy applications are unloaded. But it never took more than a few kB from swap during the whole time - although it's there.
I'd strongly recommend that you set up your software environment and about three terminals, then start profiling memory use. Look at how much extra memory use the first, second, then third terminals coming online causes (there should be no X server on the server for this test). The second and third terminals should cause roughly the same jump in memory use on the server, and the amount they've been using after they've been running for a while is probably what you want to plan for per-terminal.
Up to RAM being filled, yes, but it seems the Linux memory management has some more tricks in store :-) It means, however, that you MIGHT make your server work faster for the clients with more RAM as the memory can hold more cache etc.
Rolf
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