Host HBA settings

[jangoormans]

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.

[Richard Siemers]

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

[ilv]

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

[jangoormans]

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