Re: Oracle & RAID

I forgot to add that RAID 0+1 is best for Random I/O, which is what OLTP datafiles and index files would experience. log files are sequential I/O, and mirroring is best for sequential I/O.

Mark Tompkins wrote:

> My experience is with OLTP. Oracle recommends RAID 0+1 for OLTP. RAID 5
> is better for read only databases.
>
> One Oracle design game is to minimize disk I/O contention. The speed of
> any database application is
> ultimately dependant upon how fast the data can be written to disk (think
> parallel throughput).
>
> Spreading Oracle across lots of small disks allows greater parallel
> throughput, without causing the disk I/O system to lock up, because
> Oracle needs to write many different things in many different places at
> the same time. Remember that an Oracle instance is many processes running
>
> concurrently. Some processes want to write different things at different
> times, and different things at the SAME time.
>
> I think that it is easier to think about disk contention in terms of
> physical disks. Think in terms of platters and heads. I would think of a
> RAID array as just another physical drive. With the added benefit that
> throughput to the disk is more efficient, because of the striping (better
> parallel I/O).
>
> The Oracle 8i dba handbook goes through an exercise of designing a perfect
> system. It then discusses how to cram the perfect system into
> fewer and fewer disks. I have found this book to be the best one so far
> on the topic.
> It is weak on the discussion of RAID, and how RAID relates to the design
> sizing.
>
> Remember, Oracle recommends RAID 0+1 (striping +mirroring), rather than
> RAID 5.
>
> Redo log files should be mirrored on their own physical mirror (RAID 1).
>
> Use RAID 0+1 for the database datafiles and index files for OLTP.
>
> Use mirroring (RAID 1), if you don't have lots of cash.
>
> A minimum Oracle production OLTP database system could have at least 3
> mirrored disks.
>
> dsmcd wrote:
>
> > I've been studying about Oracle logical and physical database layouts,
> > but am
> > having a hard time understanding how RAID (probably 5 or 10) affects
> > these
> > configurations.
> >
> > What good does it do to say that certain files should be on separated
> > discs if
> > RAID is striping?
> >
> > Please be gentle, I'm still in the learning stages for both Oracle and
> > RAID.
> >
> > Any reference books or websites also appreciated.
> >
> > Oracle 8i on NT4
> >
> > TIA,
> > D.
Received on Thu Mar 29 2001 - 11:34:22 CST