based on what i see is your swap file full or not big enouf ( only 2GB ?? )
so you are using swapfile a lot
other things are fine
also can you check your traffic usage and apache status (if apache )
if a site goes slow has not always to do with the server spects , but sometimes with the programs or how you setted up the server
let me show you a screenshot of my webserver (got 12GB ram and got torrents runnig and shoutcast running and a few other things )
ignore the hd buzzy in my screenshot , it is because it is creating a backup
so all things in short
*check apache settings
*tweak mysql
*incrase temp/swap
if those are done , then it should be back fine
your hd's are fine (based on that screenshot) else you should see somehting as on my screenshot if it is your hd (it doesnt slow down my server in my case )
Greetings From PowerChaos