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Hi Chris,
Must
consider the Storage Port Maximum commands Queued. Il's Hardware limit.
I know that Hitachi Storage limit is 2048 on VSP Storage model. So
there isn’t any benefit to increasing num_cmd_elems to greater than 2048
for physical FCs connected to it. Refering to https://tuf.hds.com/instructions/performance/QueueDepth.php.
Au plaisir de vous lire (Looking forward to reading you !).
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I noticed that "high water mark of active commands" is always less than num_cmd_elems in my system, I do not know if it is true or flase. num_cmd_elems is set to 200 by default, the max of "high water mark of active commands" of 6 fcs is 180. num_cmd_elems of 4 fcs was changed from 200 to 600, all the "high water mark of active commands" became 256. The fcs is vFC card, and the num_cmd_elems of VIOS is 500, which should be set to 600 at least that waiting for service windows.
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Thanks for informing us of this, Chris. (And thanks to Dan Braden!) I've written a script which applies what you have shared. You'll find it here http://tinyurl.com/set-FC-queue-depth Hope it's a help to someone. Anthony
[Trackback] My compatriot Chris Gibson highlighted a great performance tuning attribute for Fibre Channel adapters in this blog post . I was so excited that I dusted off my blog-writing skills (much neglected) and got fired up enough to put Chris' advic
