SQL Server Performance Forum – Threads Archive

%Disk Time

Hi all, I was monitoring the performance of our SQL SERVER using perfmonitor. The data for several counters was collected for a period of 24 hours. The data collected by all the counters seemed fine and returned the values with are acceptable by norms. But the counter % disk time (which is set up against d: drive, where all the datafiles are located) is returning an average value of around 750. I have read form artiles that this counter is supposed to be under 55% (to indicate that the disk I/O is good enough). I was dubious about my calculation and tried collecting the data again for another set of 24 hours, but much to my distress, it returned almost identical value (750). Please some one let me know if I an doing some thing wrong, All I was doing was, calculating the average value of all the values returned by the perfmon. and this avegare value is 750. Do i need to do some more calculation since its a percentage or some thing ?? or is it the case that our server is having a really high I/O contention?? Thanks in advance.

Did you set adecuate scale?
How about Avg. Disk Queue Length.
Luis Martin
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The average disk Que length is 6.801 (against d: drive holding the data files, which is a RAID 5 with 16 disks on it). so it comes to 0.425 /disk which is healthy.

I had the same problem when I was monitoring my server. The %disk time was more than 100 and I was confused why the value is more than %100! The answer was that I get that number because of having multiple disks and RAID 5. <br /><br />I am not sure calculating an average for your case (750 / 16 = 46.<img src=’/community/emoticons/emotion-11.gif’ alt=’8)’ /> is a correct %disk time per disk or not.<br /><br />CanadaDBA

One to read:
http://www.sql-server-performance.com/forum/topic.asp?TOPIC_ID=7168 Also you can search (raid disk calcultation) and find some topics.
Luis Martin
Moderator
SQL-Server-Performance.com One of the symptoms of an approaching nervous breakdown is the belief that one’s work is terribly important
Bertrand Russell
All postings are provided â€œAS ISâ€ with no warranties for accuracy.

ignore % disk time, as it has no relevence for servers, all it may tell you is that you have disk activity. just pay attention to the important counters, for both reads & writes,
avg. r&w queue, avg sec/r&w, r&w/sec, r&w bytes/sec

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