While researching the effect of RAID 5 disk configuration on Oracle databases I came accrost more than I thought I expected on the topic.
With disk as cheap as it is today there is no reason to ever use RAID 5 on an Oracle database. Even for a database which sees only a moderate amount of updates the performance loss incurred by using RAID 5 is too high. RAID 1 or some combination of RAID 1 and RAID 0 should be used when high availability is required. Database 10g users should also consider allowing Oracle’s new Automatic Storage Management to handle redundancy on un-mirrored disks (or even raw partitions.)
But don’t take my word for it. Here are some opinions from some notable Oracle administrators:
Oracle Database RAID 5
No RAID5. Use RAW whenever possible and consider RAID10 or 0+1. RAID 5 can severely affect performance on highly updated databases.
Oracle Database Administration: The Essential Reference
David Kreines & Brian Laskey
RAID-5 is, in fact, very powerful and inexpensive. It is also a technology to be avoided in most cases when configuring your Oracle database! This may seem a harsh statement, but the reality is that although RAID-5 provides good levels of data protection at a low monetary cost, this comes at a very high cost for disk I/O. In particular, write operations on RAID-5 arrays can be orders of magnitude slower than the same operations on a single disk.
Oracle and RAID usage
Use RAID10 when possible, RAID5 if it is not. Size the array based on IO needs first, then storage capacity and you canâ€™t go wrong.
Disk Management for Oracle
Oracle recommends using (SAME) Stripe And Mirror Everywhere (a.k.a., RAID 1+0) for all systems that experience significant updates. This is because of the update penalty with RAID 5 architectures.
Using RAID 5 for a high-update Oracle system can be disastrous to performance, yet many disk vendors continue to push RAID 5 as a viable solution for highly updated systems.
RAID 5 is not recommended for high-update Oracle systems. The performance penalty from the parity checking will clobber Oracle performance.
If you’re still not convinced check out Baarf.com. This site is committed to the Battle Against Any Raid Five (or four or free, uh, three.) The site has links to several more articles exposing the perils of RAID 5.
2 thoughts on “RAID 5 and Oracle Databases”
Oracle is now using Apple XServes for internal use: http://www.apple.com/itpro/profiles/oracle/ based on the grounds of cheap and reliable.