Recommended average disk queue length for a RAID Array or LUN

Firstly setup a performance monitor for the RAID array or LUN and add the "Average Disk Queue" counter to the monitor. For example if our average was 10 for the RAID array and there were 6 disks in the array we could do 10 / 6 which is: 1.67 which is below 2 per disk (which is the reccomended average.)