If the system was doing well in the past then recently there are performance issues there could be a disk that is having some issue. 1 disk having some Write or Checksum errors will cause this. Check the Disk Groups from the GUI and look at the disks to see if there are any error counts happening. Run the Scrub during none business hours like start on a Friday to let it run over the weekend. In the GUI in “Diagnostics” you can see the CPU usage, Network usage and Disk usage but the most looked at is the CPU usage and look at the "Wait" this I/O Waits will be in the color of Purple when there is a high amount it is either Disk or Network, either the Network is waiting to write to the disks or the other way around, This can help to find that needle in the hay stack if you know what I mean. Another way to check things out is to use the Inspect tool, to do this you will need up29r2 or higher for the running build, example to run this is 192.168.0.220/inspect and give it a min. to load as it is running some commands, once up it will provide a great amount of details for you to review to see if there are issue with NIC, CPU and Disks.