Re: Identifying source of iowait - is it the DB or the raid array

On 6/23/05, Dennis Williams <oracledba.williams_at_gmail.com> wrote:
> Dave
>
> This is a less than expert opinion. My guess is that you won't have an
> easy time finding the answer. My guess is that certain information can
> only be found from the I/O subsystem, like your question whether it is
> the raid array cache. So you'll want to find the available information
> resources for the I/O system, and track them. But then some
> information in Oracle can provide more context to the specific
> situation, like your question like whether there are a lot of table
> scans being perfomed.
> Bottom line, I think you're going to have to act like a detective,
> gather clues everywhere, and assemble them to draw a conclusion. And
> since you won't know beforehand when an event will occur, you've got
> to gather information continually, then try to decipher the events
> that led to the event.
>
> Dennis Williams
>
> On 6/22/05, David Turner <dnt9000_at_yahoo.com> wrote:
> > Periodically we have a problem with our raid arrays
> > and suddenly iowait shoots up. Does anyone have a
> > method of identifying the source of iowait. I find it
> > hard to tell whether say the cache on a raid array was
> > disabled versus more processes performing table scans.
> > I understand historical tracking but often don't have
> > this info on the databases. Currently working with 9i.
> >
> > Thx, Dave
> >
> >
> >
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Greetings Dave,

I am assuming that its a UNIX server,

start collecting vmstat , sar and iostat with 1 sec timing and comapre the results to STATSPACK reports during performance issue , apart from other SEGMENT stats v$views ...

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Regards & Thanks
BN
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