My Microsoft Exchange server will "radomly" slow down to the point where Outlook clients will intermittently receive the message "Outlook is trying to retrieve data from the Microsoft Exchange server". When I run performance monitor on the server at these times, Average Disk Queue Length is pegged at 100%. We had an Exchange health check performed and was told everything was fine. I recently replaced the HP Smartarray controller card and the batteries are fully charged and hardware level caching is enabled. We have 3 partitions (1-100gb, 1-300gb - both on the same RAID 5 array; and an additional 200gb on a separate RAID 5 array). I know that RAID 5 isn't the "best practice" for Exchange, but, we went this route for other reasons (internal demands for journalling). Journalling is now disabled. There is more than enough disk space available. The server has 4gb of RAM, has PAE enabled, and the drives are 10K (15K would be better). Does anyone know of anything that would cause this spike of activity and slow down Outlook clients?