RN4220 prioritize maintenance tasks

We are currently experiencing service interuptions when the disk scrubbing task runs.  The unit is configured with 12 4TB disks.  It is running v6.8.1 firmware.  We have also added ram to bring the total to 20gb.  While there has been some discussion as to whether additional ram is necessary the answer is an unqualified yes.  The original 4gb was insufficient as with that amount of RAM our virtual environment was showing that the virtual machines were paused due to a loss of storage domain connectivity.  From a pure standpoint 4GB is sufficient if it is only file services being provided (NFS, SMB, FTP) once the process overhead of RSYNC, File Search and antivirus are added along with the overhead of the various housekeeping utilities, memory swapping to disk increased to the point of becoming exessive. The addition of RAM eliminated the swapping overhead and consequently the virtual machines connection to the storage domain was stabilized to provide 100% availability and the pausing issue was solved.

The question at this point is how do we set process priority so that the file sharing processes are of a higher priority than the houskeeping processes (disk scrubbing, defragmentation and disk balancing).  Defragmentation (also a memory intensive process) and disk balancing do not interfere with file sharing but disk scrubbing interferes with connectivity to the storage domain.  The 4220 is connected via 10gb/s link to a 10gb/s switch.  The virtual host machines are each connecte to the switch with 3 bonded 1gb/s ethernet links.  We have already ascertained that it is the disk scrubbing which is interferring with file services as when it is removed from the schedule the problem goes away and the problem only occurs when the disk scrubbing process is running.  The connection for the storage domain is via NFS