Managing RAID on Linux

The RAID Levels: In Depth

It is important to realize that different implementations of RAID are suited to different applications and the wallets of different organizations. All implementations revolve around the basic levels first outlined in the Berkeley Papers. These core levels have been further expanded by software developers and hardware manufacturers. The RAID levels are not organized hierarchically, although vendors sometimes market their products to imply that there is a hierarchical advantage. As discussed in Chapter 1, the RAID levels offer varying compromises between performance and redundancy. For example, the fastest level offers no additional reliability when compared with a standalone hard disk. Choosing an appropriate level assumes that you have a good understanding of the needs of your applications and users. It may turn out that you have to sacrifice some performance to build an array that is more redundant. You can’t have the best of both worlds.

The first decision you need to make when building or buying an array is how large it needs to be. This means talking to users and examining usage to determine how big your data is and how much you expect it to grow during the life of the array. Table 2-1 briefly outlines the storage yield of the various RAID levels. It should give you a basic idea of how many drives you will need to purchase to build the initial array. Remember that RAID-2 and RAID-3 are now obsolete and therefore are not covered in this book.

Table 2-1. Realized ...