performanceperformance-monitorwindowswindows 7
In the Resource Monitor of Windows 7, what does the "disk queue length" really mean?
In addition, what does the green area and blue lines stand for, as well as the response time of a program (in ms)? And why do some programs have higher response times than others?
I’m pretty sure it is the same as the Perfmon counter "PhysicalDisk _Total %time". (It tracks this counter in lock-step.)
Perfmon gives this description of that counter:
% Disk Time is the percentage of elapsed time that the selected disk drive was busy servicing read or write requests.
Basically, it is the percentage of elapsed time that the physical drive(s) were busy. So Even though your MB/s usage may be low, the % busy time can be high if the disk is heavily fragmented, or is otherwise thrashing on lots of small operations.
On a server where you would try to match the right level of high-performing disks to the workload, you would consider the disk subsystem to be a potential bottleneck if the % active (busy) time plateau-ed above 80%. On a workstation if this number is high, it just tells you that your disk performance is maybe what is slowing down your work.
As to your last question: I'm quite certain it is the physical disk and not any kernel or process time. While waiting on the physical diskthe kernel blocks whatever processes is waiting on that disk operation, and uses the CPU for whatever else needs doing.
I personally use Microsoft / Sysinternals Process Explorer.
Click on one of the four graphs at the top to bring up the current system information, then you can click on any of the peaks under the I/O bytes History graph and it will tell you what is doing the most hard drive related activities at any moment.
If however you are getting no peaks and very slow responses, it could be a sign that the hard drive is dying (or in some rare situations, faulty memory)
Best Answer
Disk queue length usually means the length (in number of I/O operations) of the queue of pending operations for a given disk. In other words, how many requests have stacked up waiting for the disk drive to be able to service them. As an example, if I can only process one request a second, but I get 6 requests in a given second, then my queue length will initially be 5 (one request is processed immediately, the five remaining must be queued).
For the meanings of the lines by color, look to the left section at the grey bar towards the middle of the top of the screen. It indicates the color and instantaneous value for each of the variables being graphed.