Profiling disk access

Question

Currently I am working on a MFC application which reads and writes in to the disk. Sometimes this application runs amazingly fast and sometimes it is damn slow. I am guessing that it is because of the disk access involved, hence I want to profile it. These are some questions in this regard:

(1).Currently I am using AQTime profiler to profile the application. Has anybody tried profiling disk access using this? or is there any other tool available which I can use?

(2). What are the most important disk parameters I should be looking at?

(3). If I have multiple threads trying to read and write the data from disk does it affect the performance? i.e. am I better off having a single threaded access to the disk?

Answer 1

You can use the Windows Performance Toolkit for this. You can enable trace providers for disk I/O events and see the I/O time and disk service time for each. It does have a bit of a learning curve though. This will also let you determine which file I/O's actually result in real-access to the disk and aren't handled by the cache manager.

Most important parameters are disk service time and queue length. Disk service time is how long the disk actually took to service the request. Queue length indicates if your disk request is backed up behind other requests.

For many threads w/ reads & writes - Many disks have poor performance in the face of reads with background writes. If you have various threads doing lots of disk I/O to random locations on the disk, you may wind up starving certain requests.