Re: Oracle & RAID

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 - 11:32:03 CST