Windows Server 2003 for 64-Bit Extended Systems
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What is the acceptable disk io queue length?

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Lee, Jones
Occasional Advisor

What is the acceptable disk io queue length?

Hi, Guys,
I have a DL380G5 runing MS Windows 2003 and MS SQL server. I find though the average disk io queue lenght is only 0.6, sometimes it will reach 160. No user complains the performace yet, but I am quite worried about that. Can anyone give some advice? Thanks a lot.
BR
Jones Lee
8 REPLIES
Igor Karasik
Honored Contributor
Solution

Re: What is the acceptable disk io queue length?

If it reach 160 only for several seconds - you don't have reason to worry

Good article about average disk io queue lenght
http://www.sql-server-performance.com/tips/monitor_io_counters_p1.aspx
Lee, Jones
Occasional Advisor

Re: What is the acceptable disk io queue length?

Thanks Karasik,
Many articals advise that when we consider the IO, we should check the number of disks in the disk array as well. In my case I have an EVA which has 72 disks inside, but several servers share it via a SAN environment. Could you advice how I can evaluate my IO performace in such case?
BR
Jones
Igor Karasik
Honored Contributor

Re: What is the acceptable disk io queue length?

>>Could you advice how I can evaluate my IO performace in such case?

You need to evaluate performance with EVA tools. We use NetApp storage, so I don't know specific EVA commands
Lee, Jones
Occasional Advisor

Re: What is the acceptable disk io queue length?

Hi, Karasik,
EVA is just an example. I hope to understand more about the way we consider the disk queue length in a big disk array or a SAN environment. Or the only way we can do is from the disk array side? Thanks for your advice in advance.
BR
Jones Lee
Igor Karasik
Honored Contributor

Re: What is the acceptable disk io queue length?

In SAN/NAS environment I never use disk queue length counter on Windows.
I check performance from SAN/NAS side
For example on NetApp I run sysstat command and see disk utilization, read latency, CPU and etc....

I assume disk queue length counter from perfmon is not accurate regarding SAN/NAS storage
Prokopets
Respected Contributor

Re: What is the acceptable disk io queue length?

Jones, you can also check disk group avg. queue length and divide id on disks qty. in disk group. If you'll get a value >2 and if the source value will be much less then a value from windows performance counter - it can be a problem.

regards,
Philipp.
Lee, Jones
Occasional Advisor

Re: What is the acceptable disk io queue length?

Dear Philipp,
Thanks for your advice. I have a disk array which has 72 disks and connected via SAN. Do you suggest me that I can divide the avg. disk queue length by 72? It sounds good for the peak time queue length (160), but a little bit odd for the small ones. Do I need also consider the array configuration such as RAID level, grouping and hot spares?
BR
Jones
Prokopets
Respected Contributor

Re: What is the acceptable disk io queue length?

Hi!
>Do you suggest me that I can divide the avg. disk queue length by 72? It sounds good for the peak time queue length (160), but a little bit odd for the small ones.
Well... As for me, the best way to find each disk queue length is to use evaperf on command view.
As for raid levels - all i said was about raid10 because a speed of raid5 HIGHLY depends on a speed of cpu in controllers and i don't know if there's a general rule, how to calculate each disk queue.