Redundant Arrays of Independent Disks (RAID) are hard to understand and are prone to bite -- there are many subtle gotchas. Vendor literature is often untrustworthy because of the hidden biases. This article contains a class on RAID devices, with particular focus on RAID 5, that can be used to sensitize yourself to the important issues. I have nothing to sell and no profit to be made from your decision, this is merely sharing the findings and approach from when I had to purchase terabytes of storage for a very large data warehouse.
The class introduces RAID 0 and RAID 1, but most of the focus is on RAID 5 as that is where the most complications exist and also where there is the largest opportunity for adjustments that the average system administrator can make that will result in dramatic improvements in performance. The introductory class covers RAID levels, RAID stripe factors, RAID tuning, the use of multiple processes against a disk, the database implications of the loss of independence of the DASD spindles, and the wisdom of using heterogeneous configurations if you have an application that requires enough RAID disk that this is possible. Unlike any other RAID background material I have found elsewhere, this explanation includes graphs showing actual (although dated) results of units of different vendors and in different configurations. (See example graph). These are included to provide a real world demonstration of particular aspects of RAID solution design or administration.
A synopsis of the article was featured in SearchStorage.com.
Do not take the specific numbers in these slides as relevant as they were taken many years ago. The numbers are off, but the general performance factors have not much changed.
Provided free of charge by Lynn Slater, Software Architecture Consultant
Download zipped PowerPoint version of the RAID 101 class
Start the RAID 101 class -- An Unbiased Introduction to RAID Storage
Excellent brief descriptions of RAID levels, collections of benchmark suites
SearchStorage's RAID info center
Discussion of hardware aspects of RAID tuning -- these are not field adjustable.
Raid Levels Explained (somewhat technospeak)
Introduction to RAID Technology (UT Austin)
RAID Advisory Board
From Design Phase (profit motive is not obvious)
RAID Technology Closes the Speed Gap Between Processors and Drives