Re: RAID Performance Issue with Oracle

Peter Marusek (pmaruse_at_hargray.com) wrote:
: I was told in Oracle school that RAID devices were not suitable for
: Oracle databases. Can anyone quantify the performance issues here?
: thanx
: Peter Marusek
:

Whoever told you this has, as usual, vastly oversimplified to effectively render this statement meaningless. A few basic issues are important here:

1. RAID is a technique for achieving data availability through various mechanisms which, in general trade off write performance against cost.
2. the most commonly used RAID techniques are either

   RAID 1: (mirroring - 100% cost penalty / no performance penalty)    RAID 5: (parity striping - ~20% cost penalty / write performance

                                                           penalty)

   but there are others such as RAID 3, RAID 4, RAID 1/0 and some even    claim RAID 7.

3 All of these techniques protect data. They may however *improve*

   performance where I/O activity is read oriented *and* where the    application can take advantage of the large muti-block reads typically    made across the many physical devices which make up a RAID stripe.

   Additionally many manufacturers go to great lengths to minimise the    write performance penalty by equipping their systems with large RAM    caches.

It is notoriously difficult to effectively profile the activity of large applications and databases on RAID systems as the number of the systems themselves vastly exceeds the number and quality of tools used to profile and configure them.

It is unfortunate, but probably true that a large number of people have been sold RAID systems and believed that they were buying performance. These same people put the system in, and application on, and found that things were worse not better. It is equally true that other, possibly better informed people went to the trouble of really understanding what they were buying and bothered to configure the application, match it to various RAID techniques and were rewarded with availability and possibly better performance.

I use RAID systems daily. On our Clariion systems, with our Oracle and Informix databases we use a mixture of RAID5, RAID1 and RAID1/0. In the eight months since we have put this system in, we have achieved excellent performance, and no down time due to disk failure.

I suggest that you contact companies such as Clariion, EMC and Storage Computer who will hopefully be able to give you a more informed opinion than your Oracle instructor.

Nick

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+    Nick Price                               Technical Consultant             +
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