Queue depth on QLogic/3par
- From: "Jeremy Schneider" <jeremy.schneider@xxxxxxxxxxxxxx>
- To: oracle-l <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 30 Jan 2008 15:53:17 -0500
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
--
Jeremy Schneider
Chicago, IL
http://www.ardentperf.com/category/technical
Other related posts:
