Re: Average physical read times

Hi Daniel

I was experiencing the exact same situation at a client (probably even worse, with sql trace reporting single block io times of up to 4 seconds for 1 block).

The root cause was determined to be a problem with the microcode on the SAN, where each LUN created would not get striped accross more than 1 rank, and would therefore consist of very few spindles. The resulting contention on the individual disks was causing those enormous latency problems.

Verify with the storage people if they're running the latest microcode on the IBM storage array.

Cheers

Stefan

On Wed, Sep 24, 2008 at 6:17 PM, Daniel Fink <daniel.fink_at_optimaldba.com> wrote:
> In a recent optimization effort, I found what I think are high physical read
> times. For example, a single block read was averaging 11 milliseconds with a
> max of over 1 second (tkprof output). For this session, single block reads
> consumed over 80% of the response time, so this is of concern.
>
> We are running Oracle 10gr1 on AIX with an IBM storage array (shared amongst
> many servers). I suspect there is some optimization that can be done at the
> storage array level. If 11 milliseconds is well above average, this will
> help in engaging that team in the process.
>
> For those of you running statspack. AWR or other monitoring tools, what are
> the average single block read times you are encountering on a good system?
> If you are running on an IBM storage array, have you found any specific
> issues/fixes?
>
> Regards,
> Daniel Fink
>
> --
> Daniel Fink
>
> OptimalDBA.com - Oracle Performance, Diagnosis, Data Recovery and Training
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Stefan P Knecht
Senior Consultant
Infrastructure Managed Services

Trivadis AG
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stefan.knecht_at_trivadis.com
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OCP 9i/10g SCSA SCNA
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