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Slow response from disk if idle
System:
Dell Latitude E6500 laptop, P8600 Core 2 Duo 2.4GHz, internal Intel ICH9M-E SATA storage interface, Windows XP SP3, Samsung HM251JJ 250GB SATA HDD, NTFS file system. Drive power down is disabled in power management profiles. Problem: Using the IOMeter disk excerciser utility, I am observing rather slow io response times (~360ms), if the drive has been idle for more than approximately 5 seconds. If the drive is accessed more frequently than every 5 seconds, every io completes rapidly. (response time in same ballpark as drive access time specification) Similar behaviour can be reproduced on an external USB drive (HP SimpleStore 1TB), however the idle timeout with this drive is 8 seconds, and the initial response time from idle is over 400ms. On a third drive, being a very old IDE drive in an USB enclosure, the problem does not occur at all. I've gone as high as 20 seconds between io's, and the response time is always rapid. The above behaviour is observed when using the "Always On" power management profile. I have been using this profile because it disables processor speed throttling. If I switch profiles to either "Minimal Power Management", or "Maximum Performance (Dell)", the response time from idle is greatly improved. For the internal drive, the typical response time is reduced to 40ms, and for the external HP drive, 60ms. (I haven’t tried the old IDE drive with these profiles yet) I thought I had found the solution, and all I would have to do now is disable processor speed throttling. Unfortunately, when I do this (using POWERCFG.EXE), the slow response times return! I am very puzzled by this. The reason I am doing this testing is that a real-time audio application that streams from disk is failing, and I believe this issue is the root cause. The application works if I generate tiny bit of background disk activity. It also works fine from the very old IDE drive, although with limited performance. I have not yet verified that the specific problem I am having is fixed by using “Minimal Power Management”, or “Maximum Performance (Dell)”). From past experience, though, processor throttling doesn’t work very well in general for this kind of application, and I should not have to use it. Any insight much appreciated. Regards, Greg. |
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