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How do I decide the value of "scsi_max_queue" in Kernel ?

 
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Keynes Lee
Regular Advisor

How do I decide the value of "scsi_max_queue" in Kernel ?

We have a Superdome server and EVA 8000 with running SAP. We created a very big LUN (1.9 TB)for SAP.

Recently, we are facing a Disk I/O performance issue. It's not possible for us to re-layout the LUN number and size.

I found some information in docs and ITRC that to increase the value ( origin is 8 ) may improve the I/O performance. And this value can be 1 ~ 255. But I just can't get any suggestions about what the exactly value shuold I set?

Would somebody please give me some direction?
6 REPLIES
Avinash20
Honored Contributor

Re: How do I decide the value of "scsi_max_queue" in Kernel ?

Please refer to the recent ITRC post which discussed the same

http://forums13.itrc.hp.com/service/forums/questionanswer.do?threadId=1320653

please dont forget to assign points
"Light travels faster than sound. That's why some people appear bright until you hear them speak."
Keynes Lee
Regular Advisor

Re: How do I decide the value of "scsi_max_queue" in Kernel ?

Thanks a lot for the rapidly response.
I found another command "scsictl" can online to modify the SCSI queue. Although ... the new setting will be reset after reboot or re-enable the VG.

My question ...
Is there any risk to run this command online ?

scsictl -m queue_depth=128 /dev/rdsk/c0t6d0

Re: How do I decide the value of "scsi_max_queue" in Kernel ?

Nope, no risk in doing that. You do realise that by using just a single LUN you are restricting yourself to just one controller on the EVA don't you? For performance purposes on the EVA you should always build volume groups out of at least 2 LUNs so you use both EVA controllers.

Are you using Secure Path or just PVLinks?

HTH

Duncan

HTH

Duncan
Keynes Lee
Regular Advisor

Re: How do I decide the value of "scsi_max_queue" in Kernel ?

Thanks !!

I have no Secure path installed. So should I run the command on each alternative PV link ???
Solution

Re: How do I decide the value of "scsi_max_queue" in Kernel ?

well you could, but generally you won't gain anything out of it, as no IO is going to go down those paths unless you have a failure. Again with just a single LUN ands PVlinks you are effectively using only 1 port out of the 8 available on the EVA8000 - not so efficient... but if you can't change your storage configuration you'll have to live with it.

HTH

Duncan

HTH

Duncan
Keynes Lee
Regular Advisor

Re: How do I decide the value of "scsi_max_queue" in Kernel ?

Thanks Duncan!!