I would definitely recommend having a secondary disk put in there. This would not be part of the raid channel - it doesn't need to be raid itself. This disk would be purely for all the ancillary stuff like temp files and logs.
Move all your system log files to /secondary/var/log
create /secondary/temp and /secondary/tmp directories
in your my.cnf file set mysql to use the /secondary/tmp dir Note that you may have to ensure the dirs have the correct rights else mysql will stop.
eaccelerator is fine but again don't let it create it's caches on disk - use shm. In php.ini set
Google for articles such as
In particular you want to make sure your file system is not slowing you down doing things like recording atime. Previously it was advantageous to check the results of hdparm to see if your disk could be tuned but with more modern disks, motherboards and recent O/S's this has already been done.
optimizing php, apache, mysql etc.
Most of these will be concerned with memory. The tendancy is to to give MySQL all the memory but that then reduces the amount of memory Linux has for caching which can cause too much swapping.
Install MySysop available from forge.mysql.com This is a great app which shows your main variable and suggests how they should be tweaked.
I'm pretty sure you will see performance gains just by adding the ancillary disk and by these simple tweaks. You still may need to upgrade in the future but at least you will know that your hardware is working more efficiently for you.
[edited by: Frank_Rizzo at 10:49 am (utc) on Dec. 18, 2006]