Here are a few of the most commonly used RAID levels

So we know what the different RAID levels do, but which level should be use for Oracle? The answers are not carved in stone but here are some suggestions, with the RAID levels listed in order of preference. Datafiles with heavy I/O requirements should use RAID 1+0 (or 0+1). It is the fastest and most secure option. If price is more of a consideration than performance, you can consider RAID 5. Most I/O operations to datafiles are buffered, with the physical writes happening in the background. As a result RAID 5 can be used to reduce costs without a significant impact on low performance systems.

Automatic Storage Manager (ASM) is Oracle's preferred solution to provide Stripe And Mirror Everything (SAME) storage. Even though ASM can provide double or triple mirroring, Oracle recommend hardware RAID is used in preference to ASM mirroring. As such, all LUNs presented to ASM are protected by hardware RAID, so ASM disk groups are defined using external redundancy and no failure groups. The Recommendations for Storage Preparation documentation provide some helpful pointers, including some of the following: - In most cases you will only need two disk groups (DATA and FRA), where DATA holds all database related files and FRA holds the fast recovery area, including multiplexed copies on online redo logs and controlfiles. Typically, the FRA disk group will be twice the size of the DATA disk group, since it must hold all backups. - Oracle recommend a minimum of 4 LUNs per disk group, with LUNs using hardware RAID and external redundancy if possible. In this case, ASM still stripes across all LUNS, but it relies on hardware RAID to provide the mirroring. - All LUNs within a disk group should be the same size and have the same performance characteristics. So don't mix LUNs of different RAID levels within a disk group. - LUNs should be made up from disks dedicated to Oracle, not shared with other applications.

As most Oracle DBAs know, rules of thumb can be misleading but here goes: - If you can afford it, use RAID 1+0 for all your Oracle files and you shouldn't run into too many problems. If you are using ASM, use this RAID level for all LUNs presented to ASM. - To reduce costs move datafiles with lower access rates to RAID 5. If you are using ASM, this may mean defining multiple disk groups to hold different files. - To reduce costs further move the other datafiles to RAID 5. - To reduce costs further experiment with moving redo logs and rollback/undo tablespaces to RAID 5. Pick the combinations that work best for your system. - If cost dictates it, move all your Oracle files on to RAID 5. For more information see: Hope this helps. Regards Tim...