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# Disk queue length performance object

Posted on 2013-01-31
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I have Dell PowerEdge server with 20 x 600GB 10RPM SAS drives in a single RAID6 array.

What is the value of Disk Queue Length performance object that would indicate a bottleneck?

I'm trying to figure if out how much this server can handle

Thank you
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Question by:piotrmikula108
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choward16980 earned 500 total points
ID: 38841776
Which poweredge, which PERC controller?

My rule of thumb is to have users create time stamps for when they experience I/O pauses by putting an icon that appends a times stamp and username.  I then go back to my performance monitor and review the disk queue length logs and see if the I/O pauses my users are reporting correlate to the log data.

quote:
"If Avg. Disk Queue Length counter exceeds 2 for continuous periods (over 10 minutes or so during your 24 hour monitoring period) for each disk drive in an array, then you may have an I/O bottleneck for that array"
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ID: 38841832
PE720XD with Perc H710 mini controller

So since I have 20 drives I could have the queue up to say 35 to be under 2 per spindle? I know I'm simplifying things...
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Expert Comment

ID: 38842566
Do you know what kind of array the 20 drives are arranged in?  Parity must be considerd as a standard RAID-5 is typically 20-25% parity overhead.
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ID: 38842587
Raid6
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choward16980 earned 500 total points
ID: 38842695
This guy says >4 for user impact:

http://www.experts-exchange.com/Software/Server_Software/Q_22868359.html

So RAID6 (20 drives - 2 ) * 600GB = 18 drives * 4 = 72.

So by that rule of thumb, >72 would = user impact.

Single controller throughput (6/Gb/s)  pci-e 2.0 (4.0/Gb/s)  so 66% of 72 = 47.52

I would assume anything > 48 would effect the user.
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