ASM and RAID. Create redundancy disk groups when using high-end storage arrays. High-end storage arrays generally provide hardware ASM and RAID protection
RAID is an acronym for Redundant Arrays of Inexpensive Disks. These provide a mechanism for load balancing and securing your data across multiple disks.
Here are a few of the most commonly used RAID levels
|–||Any RAID operation involves a certain management overhead so if your requirement is for optimum write speed and no data protection you may choose to avoid RAID.|
|0||This RAID level provides automatic block level striping of data across multiple disks to balance the load across the disk array. It provides no protection from data loss!|
|1||This RAID level is also known as disk mirroring. The RAID controller keeps a complete copy of each disk on at least one other disk. In the event of a disk failure the RAID controller switches to one of the mirrors to prevent system failure. Double or tripple mirroring can be used to provide increased levels of security.|
|0+1||As the name suggests this is a combination of RAID 0 and RAID 1, providing the benefits of block level striping across the array and the security of disk mirroring. The striping occurs across disks and the entire set is mirrored. If you can’t do 1+0, this is the best RAID option for Oracle.|
|1+0 or 10||As the name suggests this is a combination of RAID 1 and RAID 0. This sounds like it should be the same as 0+1, but it is subtly different. Each disk is mirrored individually and striping occurs across all the mirrored pairs. This is the best RAID for Oracle.|
|5||This RAID level stripes data and parity information across 3 or more disks. The parity information, which is always stored on a separate disk to its corresponding data, allows the contents of lost blocks to be derived. The significant write overhead associated with this RAID level make it slower than the previous methods, especially when a disk failure occurs, but it requires far fewer disks so it is very cost effective. In the past people have avoided RAID 5 for database applications but improvements in disk speed and controller performance mean that it is a viable solution for datafiles if performance is not a consideration.|
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.