[syslog-ng] Logs out of control

Hello, I wanted to get some guidelines on how other people are controlling their syslogs with regards to I/O performance on the database side. I am running php-syslog-ng on a separate webserver and it takes a very long time to do a search and return the results. Long time meaning 30 to 60 minutes or even longer as the logs grow. I have indexed the database by message, but it did not help. The I/O on the database server is just unmanageable. Possibilities that I'm looking into are getting 15K hard drives, change the RAID from 5 to 3, add more memory the controller's cache. Thanks, John