Measuring Queue Depth

[Computurd]

I am wondering if there is any reliable method of measuring queue depth within an operating system environment? i am using Win7 and i do not think that the operating system is measuring QD correctly, no matter what i use it does not go over two. i noticed within the anandtech SSD reviews he cites a QD workload average for different usage patterns. i am just wondering how he came to those numbers? is there a benchmark for it?

 

[ulukay]

1-2 is the normal queue depth for a single user system, especially on a SSD
higher queue depth is only reached on server systems when multiple processes are creating much workload.

 

[Computurd]

So how does the operating system assign the Queue Depth? does it change the Queue Depth according to I/O load?
also, if the average is 1 to 2 QD, why in the SSD articles does the average use run at 6.09 for light workload, medium is 3.59 and heavy is 7.76? is the information in the article incorrect??
http://www.anandtech.com/storage/showdoc.aspx?i=3702&p=12
i noticed you said especially on a ssd, but i have also tested with a HDD and received the same results, never over two.

 

[ulukay]

the queue depth is not "assigned" in any way, it's just how many commands are outstanding on your storage subsystem
meaning -> the more random IO -> the higher the queue
the slower your Storage -> the higher your queue
now you got a ssd which is fast as hell on random IOs (because of low access times) and a workload which is very light -> so you got no queued commands for your storage because your storage is not the bottleneck
some ssd benchmarks do even use a queue depth of 64, take a look at the AS SSD Benchmark

 

[Computurd]

that is the best answer i have heard describing it. thanks . others have said that it is coded into the program what the QD is... and that explanation never really meshed with me. doesnt makes sense.