Oracle and Different RAID Levels

[anuragmin]

Hi,
I came across an article on Metalink which talks about oracle and different RAID Levels.

http://metalink.oracle.com/metalink/...T&p_id=97597.1

Please go to the section
More Recommendations by Oracle RDBMS FileTypes:
(all scores are approximate, and can vary on different hardware)

As seen from the table it seems that Oracle does not recommend RAID 5 at all because thats the only place where they have given a rating of 1 (Best Performance ) for all times of datafiles only under RAID 0.

Please confirm the pros and cons of using different RAID Levels under Oracle and which one is the best.

Right now we have RAID 5 but if need be we can change it to RAID 0.

Please Suggest.

Thanks
Anurag

[marist89]

Whoa! Slow down there. Best performance doesn't necessarily mean the smartest thing to do.

RAID-0 (Striping) should NEVER be used for control files, data files, redo logs, etc. Striping gives you ABSOLUTELY NO redundancy, period. If one of your disks dies in a RAID 0 stipe set, you're toast! RAID-0 is OK for TEMP and the oracle software.

RAID-5 (Parity Striping) DOES offer redundancy. If one of your drives dies in a RAID 5 stipe set, you can still operate until that drive can be replaced. Sure, it's slower than RAID 0, but disks do fail. The more disks you have, the greater the liklihood that one will fail. RAID 5 is good for OLAP environments where the Read Rate is much greater than the Write rate. RAID 5 is a good general purpose RAID level and offers the greatest benefit for limited budgets.

RAID-1 (Mirroring) is extremely safe for database operations. However, there is extra cost because every disk has to have a disk that will mirror it's writes.

RAID-0+1 (Striping + Mirroring) is the absolute best RAID configurations for OLTP databases, hands down. However, it is also the most expensive because you are still mirroring each and every disk.

What's the best for your situation? This depends on:
1. the type of activity you will have
2. how many controllers you have
3. are you using software based RAID or Hardware based RAID?
4. your budget

[Zaggy]

I have a mixture of RAID on my larger systems, due to budget constraints. I have approx. 1 million inserts an hour on a table that has 5 composite indexes and it was all within RAID 5. I also have users doing queries back 30 to 90 days. The old configuration was a killer, becuase of the I/O contetion.

So, I moved all my partitions into seperate tablespaces, I also seperated indexes from data. Then I created a piece of software to move the old tablespaces to the RAID 5, after the intensive writes have moved onto the newer partitions. The new partitions exist within RAID 0 and RAID 1+0. The hot data resides within the RAID 1+0 and the indexes exist within the RAID 0. I am willing to accept the risk of losing my indexes and the time to recreate them, if the disks fail.

I recommend a multiple RAID solution, if you need it, but RAID 5 can work great as long as you do not have write intensive applications.