Could be some issues with the volume/array from the SW RAID 5, you might want to try using the Repair Filesystem from the Extended tools from the Console screen, this will fix any file system issues and you will be able to see the errors that it cant correct and or it could be something with the RAID, you can check the logs.

This video shows some details about the logs.

http://www.open-e.com/library/webcasts-and-videos/
2010.11 How to view and understand the log file from DSS V6