Re: Long IO Latency

On 8/16/05, Allen, Brandon <Brandon.Allen_at_oneneck.com> wrote:
> According to Oracle, the average I/O time should be < 20ms for acceptable performance. I usually see about 5-10ms on my systems - some of which are RAID10, and some are RAID5 with lots o' cache and a high (.9+) r/w ratio.
>
> 50ms is ridiculous speed and 700ms is ludicrous (slow) speed (anyone remember Spaceballs?)

Brandon,

Imagine if a particular datafile is only opened once in a statspack snapshot interval.
The overhead of opening the file would entirely occur during the single IO as far as oracle is concerned - which may be on the order of 1000 milliseconds. This is where "averages" tends to hide what is going on.

The OP should examine the individual wait events and determine if in fact there is a problem.

I agree with the numbers that you are seeing ... but have grown used to seeing under 2 ms averages when using an EMC Clarion unit (where the cache hits are likely reducing the average).

Paul

>
>
>
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Shivanischal A
>
>
> . . .
>
> Just one more question, while reading the I/O latency in the Statspack
> report, how slow is slow? I mean lets say the latency is 50ms, how do I
> determine that it is slow?
>
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