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 Post subject: Host HBA settings
PostPosted: Thu Aug 30, 2012 4:54 am 

Joined: Tue Aug 28, 2012 4:33 am
Posts: 4
Does anyone have any experience with changing the execution throttle (queue depth) on Qlogic HBA's ? I noticed that on one of our Windows 2008R2 SQL server, the execution throttle is 256, which is on the heavy side. Because the LUNs of this host were migrated from a EMC array, I suspect this setting to be sub-optimal.


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 Post subject: Re: Host HBA settings
PostPosted: Fri Aug 31, 2012 10:34 am 
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Joined: Tue Aug 18, 2009 10:35 pm
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What is your average queue depth during its heaviest load? That setting is a cap, so it will basically allow that server unrestricted access to the 3PARs available resources. Chances are the server never goes above 16 anyway... In my testing, I couldn't see a remarkable difference between 32 and 64 with IOMeter on a windows box. I imagine that 32 vs 256 would look pretty much the same, but that depends on work load type (block size, random vs sequential, read vs write). My tests were with a 8k block, 50%-50% r/w, and 50%-50% seq/random.

In situations where you have a particularly nasty application that gobbles up storage performance, so much that it impacts other (more important?) hosts that share the switch/ISLs/front end adapters/spindles, etc... you might want to intentionaly lower the queue depth on the "noisy neighbor's" adapters. I think 32 is default and a good starting point, and is the average saturation point... 16 would be the first "throttled down" setting I would use to restrict a host, followed by 8.

The 3PAR SE's should be able to help with that, since they dont have a real QOS product, they recommend using queue depth as an alternative.

Numbers are based on my testing in my environment you're mileage may vary! =)

--Richard

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Richard Siemers
The views and opinions expressed are my own and do not necessarily reflect those of my employer.


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 Post subject: Re: Host HBA settings
PostPosted: Fri Aug 31, 2012 2:34 pm 

Joined: Fri Mar 23, 2012 12:49 pm
Posts: 10
I think you can use 3Par system reporter to find out what are the peak values from your server , and then tune it to accomodate these.
Of course you can lower them even more for a glimpse of shaping rather than QOS ;)


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 Post subject: Re: Host HBA settings
PostPosted: Wed Sep 05, 2012 1:52 am 

Joined: Tue Aug 28, 2012 4:33 am
Posts: 4
Thanks for the tips. I check another host connected to an EMC CX-4, and execution throttle is the same, so I suspect 256 to be the default setting in our environment, even before introduction of 3Par


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