We have a dedicated unix server with 3 decent forums, and some small html sites that use hardly any resources.
Two are vBulletin. One is PHPBB.
It does seem like the Vbulletin forums can have a couple hundred users and it doesnt affect the server performance.
But when the PHPBB forum gets about 100 or more users, the box starts to die. Pages take 10 seconds or more to load, if they even load. Site eventually becomes unavailable.
At these 'convienient' moments the server will also decide to do some statistics software logging and generation. Or, handle a big batch of emails. Once the box starts swapping hard drive, it starts to go down until things are totally unresponcive.
Looked everywhere in cPanel to find every used resource and theres nothing obvious anymore about why it does it.
Processor #1 Name: Intel(R) Pentium(R) 4 CPU 2.00GHz
Memory: 2042768k/2088896k available (1710k kernel code, 41520k reserved, 1296k data, 228k init, 1171392k highmem)
Right now mysql is using 67.40% of the memory alone and most of the CPU usage. 76 users, 40 users, and 49 users online.
It might just be a lot for a server like ours but, sites used to run smoothly and suport hundreds of users. Cant understand why the box is dying when running only 3 forums and some small HTML based sites.