RAID 5 performance

List,

Just curious to see if most of you fellow DBA's configure your Databases on RAID0, RAID1,RAID3,RAID5,RAID1+0 or single disks. RAID 0 should get good excellent read/write performance without redundancy. RAID 1 should get good read and a fair write performance with redundancy, increased cost.
RAID 5 ????
RAID 1+0 should get an overall excellent performance for read/write with redundancy, increased cost.

RAID 5
I am very sceptical about performance.
I have an Oracle DB on RAID 5 with very poor write performance. The hardware is a Dell 650F PowerVault SAN connected to a Dell PowerEdge 6450.
The box has lots of memory, 4xCPU's connected to the Disk Array via fibre. When we perform any write operation very little memory or CPU are used. What I suspect is that our system is not configured properly therefore we see such poor
performance.

Any write operation takes 4x longer on RAID 5 compared to a local disk on the PowerEdge 6450.
I am trying to tune/configure the hardware properly before I start on the database.

The read/write caching is switched on. The memory on the SAN is 256 MB. I have tried various memory settings
for READ and WRITE without any worthwhile performance improvements. We had a "Unisys Engineer" at our site to look at the configuration of the SAN.
He was so inexperienced that he found nothing wrong with our system, he left saying that he would test the senario
on their systems and call me back the next day, he has not called in the last 4 days.

We have another smaller server running RAID 0. To create a 4GB tablespace on that server takes 1 minute 20 secs.
I am really impressed with this server.
But on our new DELL server with lots more CPU and lots more memory on RAID 5 takes 8 - 10 minutes to create a
4GB tablespace.

I know that RAID 5 had poor write performance but is it 6-8x slower than RAID 0.
I would be able to tolerate 50% performance loss with RAID 5 but not 600%. Has anyone had similar experiences with RAID 5 performance.

What is the cost implication of RAID 0+1 compared to RAID 5? If it is a matter of disks then cost should not be much of a factor because disks are
relatively cheap and becoming cheaper everyday. If you can get much better performance on RAID 0+1 vs RAID 5 with not a drastic difference in
the cost, why use RAID5?

Lots of websites say that RAID 5 is used because of the lower cost compared to other RAIDs eg. RAID 1+0.
Could u please shed some light on the cost vs performance? Are there any websites on the net that I could loot at to give me an indication of performance/cost of the various RAID disk arrays?  

TIA Best Regards

Suhen Pather
Oracle DBA
Oracle Certified Professional
Strandbags Australia Received on Tue Jan 23 2001 - 22:03:10 CST