RE: Queue depth on QLogic/3par

Yeah, the biggest thing you want to avoid is getting rejected IOs from
the storage array.  I can't speak specifically for 3par, but the
Symmetrix's architecture has got specific limitations based on how it
shuffles IOs from front-end adapters to disk adapters.  I know 3par has
some best practices guides I've seen for RH3, and I'm sure they've
updated them at least for RHEL4.  I believe they included increasing the
ql2maxqdepth parameter.

 

Thanks,

Matt

 

________________________________

From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Jeremy Schneider
Sent: Wednesday, January 30, 2008 3:53 PM
To: oracle-l
Subject: Queue depth on QLogic/3par

 

Just wondering if anyone has done much with tweaking the queue depth on
the HBA.  I'm running some benchmarks with Oracle's Orion tool
(Redhat5/Opteron/QLogic/3par) and noticed that with the small random I/O
tests the bottleneck really seems to be the queue depth - even with
hundreds of threads iostat reports sub-millisecond service time yet
shows long queues and long wait times.  Since this database being
migrated to this new system is like 95% "sequential read" from the wait
events I figure that there will be a lot of these small I/O requests and
it seems worth tuning.

There seems to be a option "ql2xmaxqdepth" on the qlogic driver that
controls the queue depth.  It defaults to 32 but I saw some chatter on
the VMware forums about increasing it to 64.  But I also saw a note for
Solaris/Symmetrix saying something about using a max queue depth less
than or equal to the max queue depth of the LUN (perhaps configured on
the SAN?) to avoid commands getting rejected by a full queue condition.

I'm not sure exactly how all of this works internally - can different
HBA's or SAN's only handle a certain max queue depth?  Has anyone else
experimented with different queue depths?  Does this change something on
the HBA or just in kernel-land?  I think I'm going to try increasing it
and re-run the Orion benchmark to see if I get any errors or performance
difference - but I'm curious what others' experience has been.

-Jeremy

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