Managing RAID on Linux

Hybrid Arrays

After the Berkeley Papers were published, many vendors began combining different RAID levels in an attempt to increase both performance and reliability. These hybrid arrays are supported by most hardware RAID controllers and external systems. The Linux kernel will also allow the combination of two or more RAID levels to form a hybrid array. In fact, it allows any combination of arrays, although some of them might not offer any benefit. The most common types of hybrid arrays, summarized in the following sections, are covered in this book.

RAID-10 (striping mirror)

The most widely used, and effective, hybrid array results from the combination of RAID-0 and RAID-1. The fast performance of striping, coupled with the redundant properties of mirroring, create a quick and reliable solution—although it is the most expensive solution.

A striped-mirror, or RAID-10, is simple. Two separate mirrors are created, each with a unique set of member disks. Then the two mirror arrays are added to a new striped array (see Figure 2-10). When data is written to the logical RAID device, it is striped across the two mirrors.

Figure 2-10. A hybrid array formed by combining two mirrors, which are then combined into a stripe.

Although this arrangement requires a lot of surplus disk hardware, it provides a fast and reliable solution. I/O approaches a throughput close to that of a standalone striped ...