I realize that many are recommending that we look at other counters like sec/Read and sec/Write instead of Avg. Disk Queue Length. However, I have a question about this particular counter:

It's typically recommended that Avg. Disk Queue Length not be greater than 2. Just as often I'll see that it should not be greater than 2 + the number of spindles in the "physical disk." This is what I'm curious about. If I'm using an external RAID system, doesn't the OS see it as one physical spindle? Would I still factor in the number of physical spindles in the array when using this counter? Some insight into how this works would be helpful.