If you are getting Stripe Group Down errors in your Xsan logs then this usually means there is a problem with your workstation accessing LUNs in the environment. This can be an issue with a given workstation having problems seeing the SAN fabric or it can be a problem with any other system seeing the fabric. You will notice the system having the error indicated in the logs. Check Apple System Profiler (keep in mind Apple System Profiler sometimes requires a reboot to refresh the LUNs it has access to via Fibre Channel) to see if the indicated LUNs are present. If all LUNs give an error (one per line) that the stripe group is down then you will typically have a bad cable, HBA, OS load or port on the switch (from the workstation or Metadata Controller). If the error is intermittent then you may have a short in one of the above devices. If all systems show the error then it is more likely the fiber (fibre) channel switch or the LUNs themselves having problems.
Happy troubleshooting!