IOWait is processes waiting on your file system to complete transfers. Look out for large number or large sized file transfers and/or a bad drive controller. If this is not a new system or new kernel and you've never had problems before, you might want to look into any new/large mysql databases.
iowait also contained network interface card communication from what i remember.
hence it might be some or all of the below :
- your mem has run out. due to mysql activity (it gulping memory) or your mysql is perfectly optimized and your connections are limited to the extent it can handle, some other activity is bogging down memory, and extensive swap is being utilized, hence youre getting hellish iowait
- theres horrendous amount of spam related network connections occuring with remote servers.