Re: storage service times
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: "Oracle L" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 3 Jan 2008 20:36:50 -0000
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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