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Using RAID5 with Oracle?

Oracle Tips by Burleson Consulting

Update - 2 February 2007

We need to note that RAID5 is only a problem for database with high DML activity, and many disk vendors have made advances that overcome the "write penalty" associated with high update activity.

One such product is the Hitachi TagmaStore RAID5 "Universal Storage Platform".  In a nutshell, the TagmaStore device uses a large 256GB cache to overcome the RAID5 write penalty.  Because this cache is so huge, the database can write to disk and move on; the parity is calculated from the data in cache asynchronously.  So unless the cache is over-extended, the database will not suffer the RAID 5 write penalty.

The TagmaStore documentation notes:

"Cache memory is memory used to perform data read/write processing efficiently between front-end and back-end directors. The cache capacity on both sides is configured to be a minimum of 4GB, to a maximum of 256GB, with expansion in units of 4GB or 8GB.

The disk controller performs control so that there is always the most efficient use of the cache in response to data access patterns, thus obtaining a highly stable level of performance.

As an optional expansion, access paths to the cache can be doubled to obtain internal data trans-mission capacities in combination with a cache switch for a maximum of 68GB/sec."


No RAID5 for Oracle

December 9, 2003

RAID 5 is universally discouraged for all Oracle database except (read-only Oracle databases) because of the huge update penalty.  Of course, database with low volumes of DML (inserts, updates) may use RAID5, so long as update response time is acceptable.

Oracle officially recommends the SAME approach (Stripe And Mirror Everywhere), essentially RAID O+1 with segregation of undo/redo and rollbacks on separate spindles.

Many of the world's most widely-read Oracle experts have become frustrated with the vendors pushing RAID-5 for Oracle.  To stop this onerous practice, they started the Battle Against Any RAID Five (BAARF) initiative:  According to the BAARF charter:

"The reason for BAARF is that we?ve had it. Enough is Enough. For 15 years a lot of the world?s best database experts have been arguing back and forth with people (vendors and others) about the pros and cons of RAID-3, -4 and -5."

Among the BAARF member are some of the world's leading Oracle experts and authors:

  • Cary Millsap - Wrote articles against RAID-5 many years ago.
     

  • Tim Gorman - Founder of People's Front for the BAARF
     

  • James Morle - Author of Sane SAN
     

  • Anjo Kolk - Has placed the BAARF logo on OraPerf.com
     

  • Rachel Carmichael - I've been fighting RAID-F for what seems like forever. Not usually winning, but fighting. Mine not to reason why, mine but to fight and die.
     

  • Brian Peasland - I've been fighting Raid-F for many, many years now. I currently have a multi-terabyte system which we want redundancy, but the powers-that-be won't fork over the cash for RAID 1 or RAID 0+1. So RAID 5 it is. I told them that data loads would take twice as long. And sure enough, they do. But they still insist on RAID 5 as the RAID level of choice. Ugh........

If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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