Re: storage service times

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
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• Original Message ----- From: "Dan Norris" <dannorris_at_dannorris.com> To: "Oracle L" <oracle-l_at_freelists.org> 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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