FreeLists / oracle-l / Re: storage service times

["Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>]

A lot of ifs go with this but:

   If your I/O pattern is even through the period
and if you've told us about almost all the I/O
and if you 8 LUNs equate to 8 separate physical
devices running at modern speeds,
then

those read times for random I/Os seem to be consistent
with the arrival rate for your random I/Os if you assume
that you are getting no benefit from caching.

The wait times are the buffer busy waits - if these are
reported as 'read by other session' (10g) then they are
also fairly consistent with the average read times.


On the other hand, your average I/O rate isn't particularly
high, and it's a little odd to get virtually indication of cache
benefit. So what else is going on that depriving you of
resources ?


Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com

Author: Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html


----- Original Message ----- 
From: "Dan Norris" <dannorris@xxxxxxxxxxxxx>
To: "Oracle L" <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, January 03, 2008 5:51 PM
Subject: storage service times


> I'm looking over a system that has what I believe to be a 
> much-larger-than-average service time for read and write I/O.
> DB 9.2.0.8
> Solaris SPARC
> VxVM/VxFS
> Hitachi (branded Sun 9990) storage array via 2xFC HBAs
> 8x 12 Gb storage array LUNs striped 256k stripe width using VxVM on the host = 
> about 90Gb volumes
> Given that (somewhat incomplete) footprint, what are your first "knee-jerk" 
> reactions to these times for a 1-hour statspack report interval:
>                 Av      Av     Av                    Av        Buffer Av Buf
>         Reads Reads/s Rd(ms) Blks/Rd       Writes Writes/s      Waits Wt(ms)
> -------------- ------- ------ ------- ------------ -------- ---------- ------
> DATA1
>       397,958     111    8.3     1.0       79,676       22      4,114    4.8
> IDX1
>       410,619     114    9.2     1.0        8,695        2    161,789    7.1
> IDX2
>       159,094      44    8.3     1.0      137,040       38         31    5.2
>
> These are rolled up to the tablespace level and I'm particularly interested in 
> comparing with other people's Av Rd(ms) (the 3rd col) and Av Wt(ms) (the last 
> col). I'll go first...my gut feeling, based on past experiences elsewhere, is 
> that 6+ ms seems about 50-100% higher than I expected to see.
> I know I'm getting service times from Oracle without offering any info on what 
> the OS or Vol Mgr say about the service times viewed from those points of 
> view, but the service time in the DB is the only metric that matters at this 
> point. I'll dig in to the other layers as necessary when I start debugging. 
> I'm looking for your opinion to see if this is a problem or if I just set my 
> expectations too high. :-)
> Thanks,
> Dan

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