TABLE OF CONTENTS Do not go where the path may lead, go instead where there is no path and leave a trail.
Ralph Waldo Emerson
As we discussed in Chapter 1, the I/O subsystem consists of many layers. The lowest layer in the architecture is the device driver that interacts with the storage hardware. Therefore, a discussion of the Tru64 UNIX I/O subsystem would not be complete without a discussion of the organization of storage and the way in which devices are managed. Because one of our ultimate objectives is to optimize the performance of the file systems and because the file systems are the upper layers in the I/O subsystem hierarchy, it stands to reason that file system performance depends on performance at the lower layers. File system performance is bounded at the top end by the performance of all the layers between the file system and the devices. Also, given this dependency, we would conclude that device management problems would cause file system problems and would ultimately be seen by the end-user applications. Experience shows us that this situation is exactly what occurs with real systems like those we examine in our coverage of case studies later.
This chapter does not attempt to make you an expert in Tru64 UNIX disk devices or drivers; however, it does provide enough background information to give readers a better understanding of how the higher layers in the I/O subsystem interact with the device management layer. In this chapter, we begin with basic...
