[eluser]tonanbarbarian[/eluser]
These sort of estimates are not easy because there are so many factors
Things like the setup of of Apache and Mysql as well as certain PHP options can all determine how well a site performs.
Given that CI is the lightest PHP framework I have seen or worked with I would suggest this box will be able to handle quite a load.
If we assume that each request is going to use up 4Mb of memory (and I have yet to build a CI app that used more than 2.5 on average). Then lets double that value to take into account the memory used by not just PHP but MySQL and Apache to handle the request.
This would mean theoretically you should have enough memory for 400+ similtanious requests.
Whether Apache and MySQL are able to be tunned to handle this is another story.
And dont forget disk. Any time you try to do multiple reads or writes on the disk it will slow things down. Fortunately Linux employes a caching mechanism that caches commonly used files into memory, but that reduces the amount of memory available to the webserver side of things etc.
I would suggest that what you have there is a good to great spec for a webserver. It is similar to the spec that lots of hosting companies would provide if you asked for a dedicated server and probably similar to what a lot of then use for general hosting as well.
If you find that it is no longer performing as well as you would like then look at the following options.
- Spreading data across multiple raid drive to reduce seek times i.e. linux core on 1 drive, website files a 2nd drive, database files on a 3rd drive, with maybe log files on a 4th drive (or turn off logging altogether)
- Move the database onto a seperate box so that the webserver can do just the one things
