System Performance Tuning2002

Disk array design is fundamentally a matter of creating a list of the most critical attributes for the environment at hand. As a result, understanding the characteristics of the environment is absolutely necessary. The following questions drive our understanding:

• Is the workload primarily read-driven, write-driven, or balanced?

• What sort of access pattern is generated? Is it primarily random or primarily sequential?

• What sort of resiliency to failure is required? How many disk failures must be tolerated? How sensitive is the environment to degraded performance in the event of a disk failure?

Think carefully about these issues as you design complex disk subsystems.

6.4.1 Choosing a RAID Level

The hallmark of RAID design is simple and important. Even though we've already said it, it bears restating.

One fairly common approach to picking a RAID level is to pick the two most important attributes in order. Then we can build the selection map shown in Figure 6-7.